Canine Chiari Malformation (CM) & Syringomyelia (SM) and the Cavalier King Charles Spaniel

Canine Chiari Malformation (CM) & Syringomyelia (SM) and the Cavalier King Charles Spaniel
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Canine Chiari Malformation (CM) and Syringomyelia (SM)  in the Cavalier King Charles Spaniel
IN DEPTH
Canine Chiari Malformation
(CM)
Syringomyelia
Symptoms
Diagnosis
MRI Clinics
DNA Testing
Progression
Treatment
Breeders' Responsibilities
What You Can Do
Research News
Related Links
CM & SM In Other Breeds
Veterinary Resources
Page 2
Page 3
IN SHORT:
Canine Chiari malformation (CM)
, also commonly known as
Chiari-like malformation
, is believed to play a major role in the cause of
syringomyelia (SM
in cavalier King Charles spaniels. While some forms of SM are known to
have other causes, this article focuses primarily upon its relationship
with CM. CM/SM is multi-factorial, and therefore identifying no single
gene mutation and avoiding it in later breedings will resolve this
disorder in the breed.
CM is a complex skull and craniocervical junction malformation
associated with a short skull, that is common in some
brachycephalic
toy
breed dogs and especially the cavalier (CKCS).  The brain is
overcrowded in the skull, and there is also
overcrowding of the spinal cord in the upper neck vertebrae. In the
CKCS, this situation
is compounded due to the cavalier having a
disproportionately large brain. The cavalier appears to have a brain more
appropriate for a bigger dog, about the size as that of a Labrador
retriever.l See
these
YouTube videos by Dr. Rusbridge
that fully explain what canine
Chiari malformation is in the cavalier.
This disproportion causes the brain, particularly the cerebellum, to
squeeze through the foramen magnum - the hole at the back of the skull,
in the occipital bone - partially blocking the flow of cerebrospinal
fluid (CSF) down the spinal cord. This both causes pain and the creation of fluid
which collects in pockets in the spinal
cord, which is what SM is. CM can cause irreversible damage to the
spinal cord, resulting in additional pain and other neurological
disorders.
SM is an extremely serious condition in which on or more
of these "syrinxes" or "syringes", develop within the spinal cord near the brain.
It is also known as "neck scratcher's disease", because one of its common
signs is scratching in the air near the neck. "Syringomyelia" is Latin for
"cavity within the spinal cord".
SM is rare in most breeds but has become very widespread in cavalier King
Charles spaniels, the Brussels Griffon (Griffon Bruxellois), and Chihuahuas. The
number of diagnosed cases in cavaliers has increased dramatically since 2000.
Researchers estimate that more than 95% of cavaliers have CM and over 50% may have SM. The severity and extent of syringomyelia also appear to
get worse in each succeeding generation of cavaliers. It is worldwide in
scope and not limited to any country, breeding line, or kennel, and experts
report that it is believed to be inherited in the cavalier.
More ...
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Symptoms
CM/SM seldom can be detected in young puppies, as symptoms of it usually are
not evident before the age of six months or years later.
Dogs diagnosed with CM and SM may have no outward symptoms at all. If
CM-affected dogs do have symptoms, they indicate pain (CM-P). The most common ones are: (a)
vocalization (barking, whining, moaning) particularly when being picked
up under the chest or when changing position; (b) head scratching or
head rubbing; (c) reduced activity, such as a reluctance to climb stairs
or jump; (d) behavioral changes, such as becoming timid, anxious, or
aggressive; and/or (e) touch aversion.
SM-affected dogs may be asymptomatic if the syrinx is small and does not
interfere with the spinal cord. Larger syrinxes -- those having a
diameter of 4 mm or more -- can damage the spinal cord and cause
symptoms such as phantom scratching, scoliosis
(see cavalier at
right)
, and weakness in the
limbs.
Pain is the most important clinical sign of CM.  Symptoms
may vary widely among different dogs, but the earliest sign often is that
the dog feels a hypersensitivity in its neck area, causing in some an uncontrollable
urge to scratch at its neck and shoulders. Then usually follows severe pain
around its head, neck, and
shoulders, causing it yelp or scream.
Click here
or the YouTube logo to see videos of cavaliers with CM/SM symptoms. As the
disease progresses, it destroys portions of the cavalier's spinal cord, and
is so painful that the affected dog may contort its neck and even sleep and
eat only with its head held high. The dog's legs may become progressively
weaker, so that walking becomes increasingly difficult.  Some dogs
deteriorate to the point of paralysis.
More ...
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Diagnosis
The only accurate way of confirming diagnosis of the disease is through the use of
magnetic resonance imaging (MRI) scanning, which can be an extremely costly procedure.
The MRI allows the veterinary neurologist to study the spine for the
presence of  any abnormality which might obstruct the flow of the
cerebrospinal fluid.   Accurate MRI results require that the dog
be anesthetized.  Clinic charges for MRI examinations of canines have
been known to vary from a rare discounted rate of $600.00 to over $2,000.00.
The names and locations of veterinary neurologists who are board
certified by the American College of Veterinary Internal Medicine (ACVIM)
are on our
Neurologists
webpage.
Chiari Check
is an
on-line questionnaire based diagnostic tool which gives a risk of
Chiari-pain and syringomyelia.
Another disorder common to cavaliers and with symptoms similar to CM/SM is
Primary Secretory Otitis Media (PSOM)
, which is a highly viscous mucus
plug which fills the middle ear and causes the tympanic membrane to bulge.
Because the pain and other sensations in the head and neck areas, resulting
from PSOM, are so similar to symptoms due to SM, the possibility that the
cavalier has PSOM and not SM should be determined before diagnosing SM.
More ...
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Treatment
Treatment options for CM/SM are very limited.  But first of all, it is
important to distinguish SM with symptoms from SM without symptoms. As a
general rule, CM/SM without symptoms (asymptomatic) should not be treated with
drugs.
Anticonvulsants, such as gabapentin
(Neurontin, Gabarone),
have been successful in some more severe cases.
Pregabalin (Lyrica,
Accord, Alzain, Lecaent, Milpharm, Prekind, Rewisca, Sandoz, Zentiva), amitriptyline (Elavil, Tryptizol,
Laroxyl, Sarotex), and oral opioids (pethidine or methadone) are alternatives.
Methylsulfonylmethane (MSM) is recommended by some veterinary neurologists
as a dietary supplement.
Drugs which reduce the production of cerebrospinal fluid, including
proton pump inhibitors such as omeprazole (Prilosec), and the diuretic,
furosemide (Lasix, Diuride, Frudix, Frusemide), and spironolactone (Aldactone),
may be useful, but clinical data on their use and effectiveness is lacking.
Carbonic anhydrase inhibitors, such as acetazolamide (Diamox) also serve to
decrease the flow of cerebrospinal fluid, but their adverse side effects of
abdominal pain, lethargy, and weakness limit long term use.
Before the disease
progresses to its severe form, the use of cortisteroids, such as
prednisolone, or non-steroidal anti-inflammatory drugs (NSAIDs, such as
Rimadyl and Metacam) may relieve the symptoms but not the deterioration.
Cortisteroids have serious side effects, such as weight, gait, and skin
changes, and harmful suppression of the immune system.  Long term use
of these drugs is not advised. As a general rule, they should be reserved
for a last resort, although some neurologists will start initial
treatment of symptomatic dogs with a combination of an anticonvulsants, such as
gabapentin, and a none-inflammatory dose of prednisolone.
Surgery to allow the cerebrospinal fluid to flow normally may be
necessary to reduce the pain and deterioration.  However, such
surgeries are technically difficult and should be performed only by
specialists.  In some cases a shunt is installed.  Although
surgery often is successful, it is very expensive, and many dogs either have
a recurrence of the disease or still show signs of pain and scratching.
The most frequent reason for recurrence reportedly is the development of
post-operative scar tissue. At least one neurologist has been inserting
titanium mesh, in an effort to prevent such scar tissue from building up.
More ...
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Breeders' Responsibilities
CM/SM has a tendency to be more severe in each subsequent generation, and
with an earlier onset.  Breeders should follow the
SM Breeding Protocol
The aim of the breeding protocol is to reduce the incidence of symptomatic
syringomyelia in the cavalier breed, and not to create litters of puppies
guaranteed not to have SM.  The chance of producing an affected dog
cannot be predicted without knowing the inheritance.
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What You Can Do
Send MRI scans of
cavaliers 5 years old or older and which do not have SM, along with MRIs of
those dogs' family members, to Dr. Clare Rusbridge at
c.rusbridge@surrey.ac.uk
When
lifting the dog, take care to support its entire body, including its
head and neck. See
this YouTube video
as an example of how to lift the dog.
Avoid
"triggers" which can prompt a CM and/or SM reaction in the dog. The main
trigger to avoid is walking the dog on a leash. Off leash exercise is
preferable.
Being
professionally groomed can be extremely distressing for CM/SM-affected
dogs, because the hands-on contact is constantly triggering.
Ease
your dog's symptoms
by using a comfortable harness instead of a collar
attached to a
leash. The neck is one of the most vulnerable regions of the dog's
body. It houses the spinal cord,  vertebrae, muscles, the
tongue bone, the thyroid gland, the trachea, the esosphagus, major
blood vessels, lymph nodes, and the thymus. Pulling on the collar
can permanently damage any or all of these vital features.
One of the best harnesses for cavaliers with CM/SM symptoms
is the
BRILLIANT K9 "Lucy Small" harness
It is easy to put on and easy to take off. Watch the videos:
"Opening the harness"
and
"Walking the dog with the harness"
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IN DEPTH:
Canine Chiari Malformation
(CM)
Syringomyelia
ymptoms
Diagnosis
MRI Clinics
DNA Testing
Progression
Treatment
Breeders' Responsibilities
What You Can Do
Research News
Related Links
CM & SM In Other Breeds
Veterinary Resources
Page 2
Page 3
Canine Chiari malformation (CM)
introduction to CM
terminology of CM
definitions of CM
cause of CM
recent CM research findings
archive of prior CM research
other factors leading to
SM
pain due to CM
For a thorough, current review of research into
canine Chiari
malformation (CM)
and its diagnosis and treatment, read
Dr. Clare Rusbridge's
June 2020 article, "New considerations about Chiari-like malformation,
syringomyelia and their management", linked here
See also,
these
YouTube videos by Dr. Rusbridge
that fully explain what canine
Chiari malformation is in the cavalier.
Introduction to CM
Canine
Chiari malformation (CM) (Chiari-like malformation)
is believed to play a major role in the cause of
syringomyelia (SM)
in cavalier King Charles spaniels. While some forms of SM are known to
have other causes, this article focuses primarily upon its relationship
with CM.
Cerebrospinal fluid (CSF)
surrounds the spinal cord and
the brain. The brain, which is relatively quite heavy,  literally
is suspended -- floating -- within the CSF, which is contained in a
three layered membrane -- a sack -- called the
meninges
This serves to  facilitate waste clearance, regulates intracranial
pressure, and also insulates the
brain from injury as it floats within it. CSF normally flows back and
forth between the brain and spinal cord with each heart beat. Disruptions
in the flow of CSF can lead to severe neurological conditions and play a
role in both CM and SM in cavaliers.
For more detailed information about CSF, watch
Dr. Clare Rusbridge's February 2025 YouTube video linked here
CM is a complex skull and craniocervical junction malformation
associated with a short (
brachycephalic
) skull, that is common in some
brachycephalic toy breed dogs and especially the cavalier King Charles
spaniel (CKCS).  The skull is too small for the brain and there is also
overcrowding of the spinal cord in the upper neck vertebrae. This is the
result of premature closure of the growth plates -- the joints between
the various bones of the skull. This is a congenital  disorder
called
"complex craniosynostosis"
. In the
CKCS, this situation is compounded due to the cavalier having a
disproportionately large brain. The cavalier appears to have a brain more
appropriate for a bigger dog, about the size as that of a Labrador
retriever.
This disproportion causes the brain, particularly the cerebellum,
to squeeze through the foramen magnum - the hole at the back of the
skull, in the occipital bone - partially blocking the flow of
cerebrospinal fluid (CSF) down the spinal cord. This both causes pain and the creation of fluid
which collects in pockets in the spinal
cord, which is what SM is. CM can cause irreversible damage to the
spinal cord, resulting in additional pain and other neurological
disorders.
CM is an inherited disorder which is rare in most breeds but reportedly has become very widespread in
cavalier King
Charles spaniels (CKCS) and the Brussels Griffon (Griffon Bruxellois) and
Chihuahuas
.  Some researchers estimate that as many as 95% of
CKCSs may have Chiari-like malformation (CM or CLM), the skull bone malformation
believed to be a part of the cause of syringomyelia, and that more than 50% of
cavaliers may have SM.
It
is worldwide in scope and not limited to any country, breeding line, or
kennel, and experts report that it is inherited in the cavalier King Charles spaniel. CM is so widespread in the
cavalier that it
may be an inherent part of the CKCS's breed standard.
2011 study
of
555 UK cavaliers, reported by their owners to be symptom-less, found 25% of one
year olds and 70% of 6+ year olds had SM. However, in
a 2015 study
of the veterinary records of 3,860 CKCSs in the UK and
Australia from 2009 to 2014, only 37 were diagnosed by MRI as being affected
with CM/SM and an additional 84 cavaliers were suspected of being affected. In a
June 2018 study
of 339 symptom-less German cavaliers, MRI scans
showed that 163 (48.1%) had SM.
CM may first appear at any age, although many dogs (up to 45%) will
develop first signs of CM before their first birthday. As many as 15% will
develop signs as of middle-age (between ages six and eight years.
CM can be progressive, in the sense that over a period of
several months, the length of the cerebellar herniation can increase
significantly. However, the severity of CM in a dog does not predict the
presence of syringomyelia in that dog. Other factors may
influence the development of a syrinx.
See Karen Kennedy's
Understanding Canine Chiari Malformation and Syrningomyelia
for diagrams of the occipital bone and foramen magnum.
Posted with
the permission of Karen Kennedy, RTMR, MappSc, a magnetic resonance imaging
specialist with The London Health Sciences Centre, London, Ontario, Canada.
She prepared these diagrams on behalf of the
Health & Education
Committee of the CKCSC of Canada
RETURN TO TOP
Terminology of CM
Caudal Occipital Malformation Syndrome (COMS)
Occipital
Hypoplasia (OH)
These four terms
-- (1) Canine Chiari malformation, (2)
Chiari-like malformation,  (3)  Caudal occipimalformation syndrome (COMS), and (4)
Occipital hypoplasia (OH)
-- have been used to identify the malformation believed to
play a role in the cause of syringomyelia.  Although they technically mean different things,
they often are used interchangeably.  Some neurologists prefer one term
over the others. However, researchers meeting at the International
Conference on Syringomyelia at the Royal Veterinary College in London in
November 2006 agreed upon the use of
Chiari-like malformation (CM or CLM)
to
describe the malformation found in the Cavalier and to a lesser extent in a
few other
brachycephalic
breeds.
More
recently,
Canine Chiari malformation
has been used to shorten and better
describe the name of the disorder. Because prior to the November 2006 London conference, CM and OH and COMS
all were used to describe the same malformation, they all are used
interchangeably in this article.
• Caudal
Occipital Malformation Syndrome (COMS)
The term, Caudal
Occipital Malformation Syndrome (COMS) had been used, particularly
by some specialists in the United States, to describe the disorder. Some diehard neurologists persist in using this term when referring to Chiari-like
malformation in cavaliers. The authors of
a 2012 German article insist that:
"... [T]he Chiari-like malformation in the Cavalier King
Charles spaniel is characterized by indentation of the occipital (bone) with
cerebellar herniation and is more correctly termed caudal occipital malformation
syndrome."
Occipital
Hypoplasia (OH)
Occipital
hypoplasia (OH)
has been used to describe the displacement of the
cerebellum into the area of the foramen magnum and a kinking of the medulla
and an indentation of the cerebellum.  "Hypoplasia" is a medical term
defined as underdevelopment or incomplete development, and so, "occipital
hypoplasia" in this instance means an underdeveloped or incompletely
developed occipital bone, which is part of the back of the skull. However,
at the November 2006 London conference, this term was rejected because there
is no proof yet that the condition is related to a hypoplastic occipital
bone.  The actual disorder is believed to be caused either by an
unusually small occipital bone or a confining membrane within the occipital
bone, resulting in the cavity in the skull containing the cerebellum to be
too small to fully contain it, leading to overcrowding of the caudal fossa
and obstruction of the neural structures, including the incomplete closure
or development of the neural tube through which flows the cerebrospinal
fluid (CSF).
In a
January 2009 article
researchers
concluded that: "While several factors are associated with neurologic signs
[of SM], occipital hypoplasia appears to be the most important factor."
However, in a
June 2012 article
German researchers compared the volumes of occipital bones of cavaliers with
and without syringomyelia and of French bulldogs. They did not find a reduced
volume of the occipital bone of CKCSs, compared to the bulldogs. They concluded: "These results do not support occipital hypoplasia as a cause
for syringomyelia development, challenging the paraxial mesoderm insufficiency
theory."
Occipital hypoplasia is to be distinguished from
occipital
dysplasia
which is an incomplete ossification of the supraoccipital bone, causing a
widening of the foramen magnum. The more
brachycephalic
is the shape of  the dog's skull, the more likely
there will be occipital dysplasia.  The cavalier is a brachycephalic
breed, and therefore a combination of both occipital hypoplasia and
occipital dysplasia can occur in the CKCS. In a
2008 German study
, the
researchers recommend that cavaliers be screened for both occipital
hypoplasia and occipital dysplasia.
In a
December 2018 article
, a team of Romanian and German researchers
used computed tomography (CT) to diagnose CM,
SM, and occiptial hypoplasia in a 21-month-old female
cavalier King Charles spaniel. CT showed a typical brachycephalic head
conformation, shortened facial bones, and a dome shaped calvarium. The
supraoccipital bone was short and stunted, and the foramen magnum
appeared enlarged, with part of the cerebellar vermis protruding.
Evidence of a syrinx was observed in the spinal cord at C2. Changes of
the occipital bone showed occipital hypoplasia with incomplete formation
of the bone
(See Fig. 6, below)
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Definitions of CM
Most Recent Definitions of Canine Chiari Malformation
Previous Definitions of Canine Chiari Malformation
Canine Chiari malformation (CM) has had a variety of definitions
over the years as more is learned about its likely causes.
Most Recent Definitions of Canine Chiari Malformation
The most recent
definition
-- in this
July 2018 article
-- attempts to include in a general
fashion all of the distortions found in the skulls of CM-affected dogs:
"CM might be described as any distortion of the skull and
craniocervical junction which compromises the neural parenchyma and
cerebrospinal fluid circulation causing pain and/or SM."
In this other
July 2018 article
, it was proposed that the disorder might be better
described as a brachycephalic obstructive cerebrospinal (CSF) channel
syndrome (BOCCS) with similarities to brachycephalic obstructive airway
syndrome (BOAS).
Canine Chiari malformation is named after a
similar condition in humans, discovered by Dr. Hans Chiari. Researchers estimate that up to 95% of CKCSs may have
CM. The back half of the cavalier's skull typically may
be too small to accommodate all of the brain's cerebellum, which may also be
too large, and so it
squeezes through the foramen magnum - the hole at the back of the skull, in
the occipital bone -
partially blocking the flow of cerebrospinal fluid (CSF) down the spinal
cord. This is called cerebellar herniation. The variable pressure created by the abnormal flow of CSF is believed
to create the SM cavities - called syrinxes - in the spinal cord.  The cavalier appears to
have a brain more appropriate for a bigger dog, about the size as that of a
Labrador retriever.
Previous Definitions of Canine Chiari malformation
Previously to 2010
, CM was defined as "decreased caudal fossa volume
with caudal descent of the cerebellum, and often the brainstem, into or
though the foramen magnum."
The 2010 definition
was "a condition
characterized by a mismatch in size between the brain (too big) and the
skull (too small). There is not enough room for the brain and the back
part (cerebellum and medulla) is pushed out the foramen magnum."
In an
October 2014 article
, UK researchers found three different definitions of
CM:
1. Indentation: "Indentation of the caudal aspect of the cerebellum
--- defined as a concave, rather than flattened or convex, caudal border
of the cerebellum."
2. Impaction: "Impaction of the cerebellar vermis into the foramen
magnum --- defined as deformation of the shape of caudo-ventral vermis
into a point such that the angle between lines drawn along the caudal
and ventral borders of the cerebellum meet at an acute, rather than an
obtuse, angle. This definition was considered analogous to descent into
the foramen magnum that has been used previously."
(In photo of a
CKCS at right, black arrow points to malformation of the caudal
fossa of the occipital bone with visualization of the vermis.)
3. Herniation: "Herniation of the cerebellar vermis through the
foramen magnum --- defined as extension of the cerebellar vermis caudal
to a line drawn between the ventral aspect of the supraoccipital bone
(opisthion) and the caudal border of the basioccipital bone (basion)."
They concluded that only the "herniation" definition distinguishes
CM-dogs because "there is a high prevalence of cerebellar indentation
and impaction in the normal canine population, suggesting they are
unreliable as defining factors for CM."
However, even prior to that change, in a
February 2014 article
, a neurology team studying the Griffon
Bruxellois (Brussels Griffons) recommended a redefinition of CM,
explaining:
"This study supports the view that CM is a multifactorial condition
that includes the shortening of the entire basicranium, loss of
convexity of the supraoccipital bone, invagination of the cerebellum
under the occipital lobes and possibly by increased proximity of the
atlas to the occiput. As a compensatory change, there is increased
height of the rostral cranial cavity and lengthening of the dorsal
cranial vault. Overcrowding in the caudal cranial fossa and the
craniocervical junction is a defining feature. The study provides the
basis of a quantitative assessment of CM which might identify risk of
syringomyelia and suggests that CM should be redefined so that account
is taken of the overcrowding of the entire cranial fossa and
craniocervical junction with reorganization of the brain."
In a
March 2016 study
of Griffons Bruxellois, the
definition was tweaked again, and this time, much more complexly worded,
as follows:
"a more global cranium and craniocervical
junction abnormally characterized by insufficiency of the supra and
basioccipital bones with compensatory rostral cranium doming, shortening
of the skull base and increased proximity of the cervical vertebrae to
the occiput resulting in overcrowding of the neural parenchyma in the
caudal fossa."
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Cause of CM
Why
does the cerebellum squeeze through that hole?
Why is the
skull too small for the brain?
Why do the
growth plates close prematurely?
Why cavaliers?
Canine Chiari malformation can be very deceiving, because the obvious
problem it causes is that the cerebellum squeezes through the foramen
magnum, which is the small hole at the back of the skull in the
occipital bone. As noted above,
definitions of CM prior to 2010
were limited to describing that
specific condition. But that is only a consequence of CM -- the end
result of it -- and does not explain its cause.
Why does the cerebellum squeeze through that hole
Beginning in 2010
, an answer has been
that the skull is too small for the brain, causing overcrowding of the
brain, with that hole being the path of least resistence to that
overcrowding. But that, too, is only a consequence of CM and not the
underlying cause.
Why is the
skull too small for the brain
The current answer to that
question is a developmental defect which has been labeled "complex
craniosynostosis". Complex craniosynostosis is the premature closure of
the growth plates which are the joints between the various skull bones.
Growth plates in the skull are called cranial sutures, which are fibrous
joints which remain flexible as the puppy's brain grows in size and then
gradually fuse their adjoining skull bones together. When these growth
plates close prematurely, the size of the skull does not accommodate the
growing brain, and so the brain and skull become mismatched with the
skull being too small for the brain. This overcrowding of the brain
causes it to rotate to an unintended position within the skull,
resulting in brachycephalia as well as CM. So,
the definition of CM evolved in
2018
to incorporate these findings.
The next question is:
Why do the
growth plates close prematurely
It
clearly is a congenital disorder, since it occurs at birth and during
the developmental stage of the puppy's skull and brain. It is so common
among cavalier King Charles spaniels that it must be genetic in the
breed. Finding the answer to that question remains to be done, and
perhaps once it is answered, the definition of CM will change again.
Finally, the question arises:
Why
cavaliers
Assuming for now that the cause
in CKCSs is genetic, the breed-specific cause may be due to efforts by
cavalier breeders to conform it a defined "breed standard", particularly
one associated with the definition of the shape of the head. The direct ancestors
of the CKCS have been around since as early as the 1500s. Paintings over
the past 500 years have shown toy spaniels having a variety of head
shapes, but
mostly
(with notable exceptions) with fairly pointed
(snipy) muzzles until the mid-1800s and
much more shortened ones beginning in the early 1900s. This early-1900
version has persisted since then and is the current head shape of the
King Charles spaniel (English toy spaniel). Then beginning in 1926 an
effort was made by some UK breeders to re-establish the somewhat longer
muzzle of the mid-1800s. (See
Origin of the Breed
.)
The current breed standard definition of the proper head shape of a
cavalier is derived from the efforts of those late-1920s breeders to
produce the longer muzzle. Specifically, the UK Cavalier Club's breed
standard describes the ideal CKCS head shape as:
Head and Skull:
Skull almost flat between ears. Stop shallow. Length
from base of stop to tip of nose about 3.8 cms (1½ ins). Nostrils black
and well developed without flesh marks, muzzle well tapered. Lips well
developed but not pendulous. Face well filled below eyes. Any tendency
to snipiness undesirable."
Other nations' cavalier clubs' breed standards describing the proper
head are very similar if not identical. So, over the past 500 years, the
cavaliers' ancestors have gone from pointed (snipy) muzzles with fairly
narrow heads to almost pug-shaped heads with exaggeragted domes of the
early 1900s to the more moderate muzzles and wider skulls since 1926.
These efforts have caused a sharp reduction in the gene pool of the
breed, and particularly very likely several genes associated with the
head, including the skull and the brain.  Geneticists have found
that when you encourage the mutation of one gene to achieve a certain
specific result, you may end up with all sorts of other genetic
consequences, called the
"hitch-hiking effect"
. See
this
February 1974 article
So, the cavalier breeders did not intentionally seek to create a
breed with "a head too small for its brain", but with the hitch-hiking
effect of mutated genes, that may be with what they ended up.
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Recent CM research findings
(2015 - 2025)
In
February 2021 article
, neurology researchers Clare Rusbridge and
Penny Knowler point out that there is increasing evidence that
brachycephaly disrupts cerebrospinal fluid [CSF] movement and
absorption, predisposing CM and SM. They show how the reduction of the
lymphatic absorption of CSF through the lymphatic system organs located
in the nasal and skull base, combined with the restriction of CSF
movement through the junction of the skull with the spinal cord, appear
to be key consequences of extreme brachycephaly in dogs and explain the
likely causes o f these neurological disorders. Specifically relating to CM and SM, they state:
"Cavalier King Charles spaniels with syringomyelia associated with
Chiari-like malformation have smaller volume jugular foramina compared
to Cavalier King Charles spaniels without syringomyelia. However, direct
causality between smaller jugular foramen and syringomyelia has not been
proven. ... [C]raniosynostosis [premature closure of cranial sutures,
preventing continued growth to accommodate the growing size of the
brain] may be associated with a primary venous abnormality. Cavalier
King Charles spaniels with syringomyelia associated with Chiari
malformation have reduced volume caudal cranial fossa dorsal sinuses.
... Chiari-like malformation associated pain in dogs describes a
syndrome of pain associated with brachycephaly and hindbrain herniation.
It is often compared to Chiari type I and 0 malformation in humans.
However, it is more like the hindbrain herniation seen with syndromic
and complex craniosynostosis in humans, for example, Crouzon's and
Pfeiffer syndrome."
"In comparison to dogs with Chiari-like
malformation only, dogs with syringomyelia have more extreme
brachycephaly with craniocervical junction deformation, including
cervical flexure, change in angulation of the odontoid peg, increased
proximity of the atlas to the skull (often referred to as
atlanto-occipital overlapping), kinking or elevation of the craniospinal
junction, and loss of the cisterna magna. Changes in conformation of the
spinal canal and cord may also contribute. The authors propose that
syringomyelia develops due to a combination of reduced CSF absorption
though nasal lymphatics, reduced venous drainage, altered
neuroparenchymal compliance, and reduced CSF movement through the
lateral apertures or craniocervical junction. Curvature of the spinal
canal and intrathoracic pressure gradient may contribute especially in
the thoracic spinal cord. The mechanism of development of syringomyelia
is controversial. The most accepted theory is that subarachnoid space
obstruction results in a mismatch in timing between the arterial pulse
peak pressure and CSF pulse peak pressure."
In a
November 2019 article,
a team of UK researchers reviewed the medical records of
66 cavaliers, 40 of which had syringomyelia
(SM) and the other 26 did not; 55 had Chiari-like malformation (CM) and
11 did not. The dogs were grouped by (1) control group of 11 with no
Chiari-like malformation (CM-N); (2) CM pain group (CM-P) of 15 dogs;
(3) clinical SM group (SM-S) of 40 dogs. SM-S dogs included those with
outward symptoms of SM (variable phantom scratching, scoliosis, etc.)
and a syrinx of at least 4 mm. The researchers divided their study into
two sub-sets, the first examined head features related to the dogs' soft
palates, and the other examined features related to their hard palates;
both sub-sets also included review of the dogs' features related to
forebrain flattening and olfactory bulb rotation. The olfactory bulb is
a bulb of neural tissue within the dog's fore-brain. Their work included
comparing the shape of the "stop" of each dog, which is the degree of
the angle where the nose and skull meet, and the indentation between the
eyes at that point. A "gentle stop" has the least angular shape and a
"pronounced stop" has the sharpest angle.
They found
(see figure 5 below)
• CM-N dogs (no CM) had the least brachycephalic head, a gentle stop
with the greatest upper jaw area between the hard palate and the frontal
bone, and the longest soft palate length.
• CM-P dogs (painful CM)
had the least distance between the hard palate and cranium, a pronounced
stop, and a displaced olfactory bulb.
• CM-S dogs (large syrinx) had
the most reduced middle craial bone area and shortest distance between
the connection of the hard and soft palates with the base of the
cranium.
They conclude that dogs with CM-P had the shortest muzzle lengths,
and that "a reduced distance between the hard palate and the frontal
bone was particularly associated with CM-P." Dr. Clare Rusbridge, one of the
researchers, explained:
"Dogs with clinically relevant CM/SM are
more likely to have brachycephalic features of the rostral skull
flattening with reduction of nasal tissue and a well-defined stop. This
evidence not only enhances our understanding of the disease and 'at
risk' head conformation but could also impact on the assessment of MRI
and disease diagnosis. It suggests the whole skull should be analyzed
and not just the hindbrain currently required in prebreeding screening.
This information has implications not only for breeders and pet owners
but also for the veterinary profession to raise awareness about the
welfare aspects of breeding. Furthermore, an increased risk for SM and
painful CM might not be confined to brachycephalic breeds but other
miniaturized purebreeds and hybrids that have gained in popularity as
pets."
Co-researcher Dr. Susan P. Knowler explained:
"This study suggests that the whole skull, rather than just the
hindbrain, should be analysed in diagnostic tests. It also impacts on
how we should interpret MRI from affected dogs and the choices we make
when we breed predisposed dogs and develop breeding recommendations. ...
The
brachycephalic features that can be seen from outside is a head that has
flattening at the front with reduction of nasal tissue and a
well-defined stop."
In a
September 2019 article
, a team of UK neurology researchers used
"machine-learning" to identify biomarkers which distinguish between
cavaliers with and without pain due to Chiari-like malformation (CM-P)
and also those with and without syringomyelia (SM). Thirty-two CKCSs
were included in the study, of which 10 had pain due to CM, 11 had
symptomatic SM (SM-S), and 11 controls which had neither CM-P nor SM.
"Machine-learning" is a process of a computer not explicitly programmed
by people, which looks for patterns and data, then analyzes that
information and draws conclusions and makes predictions from that
gathered information. In this case, the machine looked for morphological
changes in the dogs, which may not be apparent to human observers,
thereby removing potential bias or blindness that may be produced by a
hypothesis driven expert observer approach. The machine learning
approach was to understand neuromorphological change and to identify
image-based biomarkers in dogs with CM-P and and symptomatic SM (SM-S).
Upon comparing dogs with CM-P or SM-S to the control group, candidate
biomarkers were identified in specific regions of the brain for CM-P and
for SM-S, particularly between the presphenoid bone and area between the
soft palate and the tongue, which they concluded indicates both
conditions being strongly related to changes within that area. This is a
very preliminary study aimed at developing these biomarkers into a
clinical diagnostic test.
In an
April 2019 abstract
, a team of UK neurology researchers (Eleonore
Dumas
[right]
, Susan Penny Knowler, Felicity Stringer, Clare
Rusbridge) examined MRI scans of 66 cavalier King Charles spaniels,
including 11 without either syringomyelia (SM) or painful Chiari-like
malformation (CM-P), 15 with only CM-P, and 40 with clinically severe
CM/SM. They report finding that the SM-affected CKCSs "had a more
ventral orientation of the olfactory bulbs and shorter distance between
basicranium and hard palate." They concluded that cavaliers with
symptomatic CM/SM are more likely to have brachycephalic snouts and
"'midface' hypoplasia similar to craniosyostosis Crouzan syndrome."
In a
January 2019 article
by a team of UK and Swedish researchers
(Susan Penelope Knowler, Lena Gillstedt, Thomas J Mitchell, Jelena
Jovanovik, Holger Andreas Volk, Clare Rusbridge), 13
cavalier King Charles spaniels were examined by UK breed judges, using
checklist
, to determine if the risk of Chiari-like malformation (CM) and
syringomyelia (SM) could be identified by visual assessment of head
shape. The results showed a positive correlation between the judges'
evaluations and the risk of CM/SM sufficient to warrant a larger study
of the breed. Figure 5 (
below
) shows the most extreme range of checklist
scores. The researchers concluded:
"This prospective investigation demonstrated that it was possible to
compare subjective evaluation of head conformation with objective
measurements and revealed a significant correlation between the
subjective visual evaluation of head conformation and an objective
evaluation of dorsoventral doming using photographs. However, this pilot
investigation demonstrated that individual adjudicators can vary in
their interpretation of the CKCS breed type and also suggests that
measuring the cephalic index or rostrocaudal doming alone is not a
reliable indicator of brachycephaly but should be taken together with a
visual evaluation and take account of other features, such as those on
the checklist and the size of the dog."
In a
July 2018 article
, Dr. Susan (Penny) Knowler (and Gabriel L.
Galea, Clare Rusbridge) reviews over 20 years of neurological research
into the conditions of Chiari-like malformation (CM) and syringomyelia
(SM) primarily in cavalier King Charles spaniels (CKSC) and a few other
brachcyphalic breeds. She covers the key morphocenetic processes
involved in CM/SM, including (a) anatomical abnormalities, (b)
brachycephaly, (c)cranio-cervical junction abnormalities, (e) embryology
(fetal development), (f) the brain and ventricles, (g) the skull, and
(h) genetics of CM. She provides a current defintion of CM as:
"a
malformation of the skull and craniocervical junction which compromises
the neural parenchyma to cause pain and/or disrupt CSF circulation which
can result in SM."
In a
January 2017 article
, the UK researchers further pursued their
analysis of CM resulting from an overall disorder of the conformation of
the CKCS brain and skull. They stated:
"Thus, CM is not just a reduction in the cranial base and caudal
fossa. The `ellipticity' of the brain provides a quantitative value to
compare the natural oval shape of the Control cohort to the more global
brachycephalic CM pain and two SM cases. The reduced size and rotation
of the olfactory bulb, together with the clival angle (cranial base
angulation between the ethmoidal plane and the clival plane), is
associated with a shortened muzzle and increased stop and a `face' that
tilts up like a human. ... The
morphing movie (S1 Movie)
highlights the dynamic changes of the
skull conformation and brain parenchyma associated with progressive
brachycephaly and airorhynchy, shortening of the basicranium and
supraoccipital bones and the proximity and angulation of the atlas and
dens."
Describing cavaliers specifically, the researchers stated:
"Ten of the fourteen significant variables were found in the CKCS
with one, line
a-c [see red line a-c in the diagram below]
, unique to the breed.
Line
a-c
indicates the proximity of the sphenooccipital
synchondrosis to the atlas bone. This study confirms the findings of
others that the CKCS with SM have a reduced caudal fossa size a presumed
consequence of early closure of the spheno-occipital and possibly other
cranial sutures. Compared to other breeds including the GB, the CKCS has
considerably greater incidence of cerebellar deformation by the
supra-occipital bone and vermis herniation. These findings and the
coexistence of occipital dysplasia and hypoplasia suggest that the CKCS
may have additional predisposing risk factors for SM compared to the
other breeds."
In an
April 2016 abstract
, UK neurological researchers found evidence that
CM may be the result of an overall disorder of the conformation of the
CKCS brain and skull. They examined MRI scans of the skulls of 70
cavaliers, divided into four categories: SM with phantom scratching (15
CKCSs); clinical SM (e.g. pain) but no phantom scratching (17 CKCSs);
behavioral signs of pain with CM but no SM (25 CKCSs); and CKCS with no
SM and no behavioral signs of pain or scratching (13 dogs -- "CKCS
control"). They also had an "other-breed-control" group of 19 dogs
(including 5 brachycephalic -- short-muzzled), with normal brain sizes.
They
hypothesized that there may be insufficient room within the skull for
the
forebrain
, and that may contribute to backward displacement and
overcrowding of the
hindbrain
. They focused upon the forebrain's
olfactory bulb (OB -- also called olfactory lobe), which is at the lower front of the forebrain and
directly behind the olfactory receptor cells in the dog's nose.  The more brachycephalic (short-muzzled) the dog, the
more the OB tends to be lower and the more the frontal lobe tends to be
flattened against the front of the skull.
(Compare the normal
location of the canine forebrain in the diagram at the left, with the
flattened frontal lobe and the lower olfactory lobe of a CM/SM-affected
cavalier, at the right.)
They found that the
more severe the CM/SM condition of the cavaliers in the study, the
smaller the mean size of the OB, and that there was a significant
difference between the cavaliers in the four CM/SM groups and the
dogs in the other-breed-control group. They also noticed a trend towards
more ventrally (lower) orientated OB with increasing CM/SM severity. They concluded:
"This study suggests that CM should be considered a more global brain
and skull conformational disorder with features of extreme brachycephaly
including smaller more ventrally orientated OB; however, further work is
required and the measurement technique has been refined for future
studies. We recommend that future studies into MRI conformation of CM
and SM uses rigorous phenotyping based on clinical signs and age."
In an
April 2015 article
on the subject of the kinking (or elevation) of the medulla,
researchers examined 36 cavaliers (33 having canine Chiari malformation and 26
having
syringomyelia)
and reported finding that higher elevation of kinking of the medulla
related to neurological clinical signs of CM/SM. They also found that
brainstem position measurements at the caudodorsal-most border of the
fourth ventricle (called the "obex position") were associated with both
the presence and severity of syringomyelia. An obex position measurement
of ≤3.5 was sensitive (79%) and highly specific (90%) for the presence
of syringomyelia.
(The photo at right from the
April 2015 article
shows how the position of the brainstem was
evaluated by measuring the distance between the obex (the
caudodorsal-most border of the fourth ventricle) and a line drawn
parallel to the foramen magnum. This was termed the "obex measurement".
RETURN TO TOP
Archive of prior CM research
There is not yet a consensus among veterinary investigators as to how to
measure the cavalier's occipital bone to determine what should be the shape
of the cerebellum within a "normal" CKCS's occipital bone.
Dr.
Clare Rusbridge
BVMS, MRCVS, PhD, DipECVN (right), of the Stone
Lion Veterinary Centre in London, England, a leading investigator into SM,
has described the three "classic features" of canine Chiari
malformation as:
(1) loss of the normal round shape of the cerebellum, which can appear to be
indented by the occipital bone; (2) displacement of the cerebellum into and
through the foramen magnum, i.e. herniation; and (3) kinking of the medulla.
2009 and 2010 UK studies in which Dr. Rusbridge later participated
(discussed below) suggest that caudal fossa volume may also play a role in
CM.
In a
2006 study
conducted by
Dr. Natasha J. Olby
and
Dr. Sofia Cerda-Gonzalez
, both board certified
veterinary neurologists, and others at North Carolina State University's
College of Veterinary Medicine's Department of Clinical Sciences and the
IAMS Pet Imaging Center in Raleigh, NC., they have concluded that the
incidence of caudal fossa and cervical spinal abnormalities is high in
Cavaliers, and that the pathogenesis of syringomyelia is multi-factorial
rather than due to a single malformation.
In a
2009 Scottish study
led by Dr. Jacques Penderis, of 70 cavaliers and 80 dogs of
other breeds, the researchers found that "all [of the] CKCSs had
abnormalities in occipital bone shape. ... CKCSs had a shallower caudal
cranial fossa and abnormalities of the occipital bone, compared with those
of mesaticephalic dogs. These changes were more severe in CKCSs with
syringomyelia."
However, in a
January 2009 article
Drs. Sofia Cerda-Gonzalez, Natasha J. Olby, Susan McCullough,
Anthony P. Pease, Richard Broadstone, and Jason A. Osborne
failed to find the same association when comparing the caudal fossa of CKCS
with and without syringomyelia using three-dimensional measurement methods.
Research journal articles published in 2009 and 2010
point to evidence that cavaliers' hind-skull volumes are not different from
other small breeds, particularly those with short muzzles, and that the percentage of the volume of the caudal fossa -- the hind-skull cavity --
to the volume of the total cranial cavity, did not differ significantly between
those CKCSs with and without SM.
However, these studies also found that the volume of hindbrain within the
hind-skull was significantly greater for young -- 2-years and younger --
cavaliers with SM than older dogs -- 5 years and older -- without SM.
They also found that increased hindbrain volume in CKCSs with SM, compared
to that of the hind-skull, was directly correlated with the size of the
dogs' syrinxes.
The first of these investigations was a
2009 German
study
of 40 cavaliers and 25 dogs of other brachycephalic breeds. The
researchers found that: (1) "All CKCSs had cranial characteristics
consistent with CLM"; and (2) "There were no significant differences between
CKCSs and brachycephalic dogs with respect to the ... volumes of the CF
[caudal fossa
] ...". They concluded: "Results of this study suggested that
descent of the cerebellum into the foramen magnum and the presence of syringohydromyelia in CKCSs are not necessarily associated with a volume
reduction in the CF of the skull."
The caudal (
for "rear") cranial fossa is part of the cavity within the skull. It
contains the brainstem and cerebellum, and towards its rear, it is enclosed
by the occipital bone, which also frames the opening called the foramen
magnum.
Similarly, in a
2009 UK study
comparing the cerebral cranium
volumes of the CKCS with those of other small breeds and the Labrador
retriever, Hannah Cross and Drs. Rusbridge and Rodolfo Cappello
found that cavaliers
do not
have a proportionately smaller caudal fossa
compared to other small breeds, but that the CKCS's brain is comparatively
large.
In that 2009 UK study, the researchers stated:
"When compared with Labradors, CKCS had proportionately
the same volume of parenchyma [hindbrain] in their caudal fossa [skull], hence there is a
mismatch of volumes with too much parenchyma in a too small caudal fossa
causing overcrowding. ... Other small breeds of dogs had a proportionately
smaller volume of parenchyma in their caudal fossa which can explain why,
despite having a similar sized caudal fossa to CKCS, they do not experience
overcrowding. It is hypothesised that through the miniaturisation process of
other small dogs, both the cranium and brain are proportionately smaller but
in CKCS only the cranium has reduced in volume, hence why there is a higher
incidence of CM in CKCS than other small breeds.
"Cavalier King Charles spaniels also had a greater
percentage of their cranial fossa filled with parenchyma (cranial fossa
parenchyma percentage) compared with small breeds and Labradors which had a
similar percentage. Overcrowding in CKCS might therefore occur due to a
mismatch in volumes in both the caudal fossa and cranial fossa of the skull,
suggesting the cranial fossa is also involved in the pathophysiology of CM."
They conclude:
"The results support mesoderm
insufficiency or craniosynostosis
**
as the pathogenesis of Chiari-like
malformation (CM) in CKCS. It presents evidence for overcrowding of the
caudal fossa due to a mismatch of brain parenchyma and fossa volumes as to
why CKCS and not other small dogs are affected."
The mesoderm is the middle of the
three primary germ cell layers -- the others being ectoderm and endoderm --
in the early stage of an embryo. The mesoderm is responsible for developing
various tissues and structures, such as bone, muscle, connective tissue, and
the middle layer of the skin. Mesoderm insufficiency
during embryology may cause insufficient scope for the mesoderm and ectoderm
layers to develop
**
Craniosynostosis
is a developmental abnormality in which the immature skull's growth plates
prematurely fuse, changing the growth pattern of the skull.
This suggests both a possible genetic cause of the
displacement of the cerebellum through the foramen magnum, as well as evidence
that the cavalier's skull may not be too small, but that its hindbrain is too
large, hence the "mismatch".
To the contrary, however, in a
2009 Scottish study
led by Dr. Jacques Penderis, of 70 cavaliers and 80 dogs of
other breeds, the researchers found that "all [of the] CKCSs had
abnormalities in occipital bone shape. ... CKCSs had a shallower caudal
cranial fossa and abnormalities of the occipital bone, compared with those
of mesaticephalic dogs. These changes were more severe in CKCSs with
syringomyelia."
The posterior
(or caudal -- for "rear") cranial fossa is part of the cavity within the
skull. It contains the brainstem and cerebellum.
The
JSAP 2010 study
researchers found that a cavalier with a higher volume of hindbrain within
the skull is more likely to have SM, and the greater the volume of
hindbrain, the larger the syrinx. They also found a direct relationship
between between the dimensions of the brain ventricles ("ventriculomegaly"
--
see below
) and the size of
the syrinx.
In addition, the
2010 JSAP research
suggested that
there may be a "failure of communication" between the paraxial mesoderm
and
the cranial somites
**
with the closing neural tube
***
in the embryo, resulting in loss of coordination between
the growth of the skull and
the hindbrain. When functioning properly, the growth of the mesoderm
supports and helps to facilitate the closure process of the neural tube.
They concluded that overgrowth of the cerebellum in the embryo may cause the mis-match,
because cavaliers have proportionately more hindbrain volume than other
small breed dogs. They stated:
"Early growth plate closure may result in CM because despite the dynamic
nature of osseous tissue, it would be unable to accommodate the developing
brain."
Paraxial mesoderm  forms the supraoccipital
bone.
**
Cranial
somitic mesoderm forms the exoccipital and basioccipital bones.
***
The neural
tube in the embryo develops the brain and spinal cord
Then, later in 2010, the authors of the 2010 UK JSAP report presented
an abstract
before the 2010
congress of the British
Small Animal Veterinary Association (BSAVA), in which they re-affirmed
that, while SM occurs in cavaliers which have CM, it is the
mis-match
between the volumes of the hindbrain and the hind-skull which is believed
to actually lead to SM, if not be the cause of SM. In that abstract, the
authors go on to conclude that the more marked volume mis-matches they found
between the hindbrain and the skull, the more severe the SM which
affected the young dogs -- under 2 years of age -- in the study.
In a
December 2010 UK study
led by Colin Driver, the researchers' results were
consistent with the previous findings that ventriculomegaly and a small but
significant increase in caudal fossa parenchyma are associated with
syringomyelia. Further, this December 2010
study also found that the volume of the skulls of CKCS under 2 years of
age and SM-affected were significantly smaller than the skull volumes of
cavaliers over 5 years of age and SM-clear.
The UK studies in 2009 and 2010 suggest
that a disproportionately large hind portion of the brain may
be a necessary element of SM in the breed. These 2009 and 2010 research
reports explain why CM has been re-defined as "a condition characterized by
a mismatch in size between the brain (too big) and the skull (too small).
There is not enough room for the brain and the back part (cerebellum and
medulla) is pushed out the foramen magnum."
In a
June 2011 study
, which included Drs.
Rusbridge, Driver, and McGonnell, they reported that twelve CM-affected cavaliers'
foramen magnums and the length of cerebellar herniation "increased
significantly" between MRI scans 9.5 months apart. they concluded:
"This work could suggest that overcrowding of the caudal
cranial fossa in conjunction with the movements of cerebrospinal fluid and
cerebellar tissue secondary to pulse pressures created during the cardiac cycle
causes pressures on the occipital bone. This leads to a resorption of the bone
and therefore an increase in caudal cranial fossa and foramen magnum size
allowing cerebellar herniation length to increase."
"the CKCS has a relatively larger cerebellum [in purple
at right] than small breed
dogs and Labradors and there is an association between increased cerebellar
volume and SM in CKCS. In contrast to small breed dogs and Labradors, CKCS
exhibit correlation between increased cerebellar volume and cerebellar crowding
within the caudal CCF, suggesting that CCF growth in CKCS is not keeping pace
with the growth of the cerebellum.
"These findings support the hypothesis that it is a
multifactorial disease process governed by increased cerebellar volume and
failure of the CCF to reach a commensurate size."
They also found:
(a) "CKCS under the age of 2 with SM have an increased
cerebellar volume when compared to CKCS over the age of 5 without SM. This
supports hypothesis that increased cerebellar volume in CKCS is associated with
syringomyelia. Previous volumetric studies in CKCS have shown that there is an
association between SM and CCF parenchyma volume, but this is the first time
that cerebellar volume has been linked to SM. The cerebellum to brain volume
ratio is consistent between normal dogs and has been shown to decrease with
cerebellar degenerative disorders, but it has never been shown to be increased
in size in a canine neurological disorder."
(b) "The degree of cerebellar crowding in the caudal CCF is
correlated with increased volume of the cerebellum in CKCS, and this is not seen
in small breed dogs or Labradors."
(c) "The degree of crowding may determine the degree of
foramen magnum obstruction, and in turn the tendency for syrinxes to form.
Cerebellar volume is potentially a key factor in determining the degree of
obstruction and interference in normal CSF flow through the foramen magnum,
which disposes dogs to the subsequent development of SM."
(d) "In CKCS an increase in relative cerebellar volume is
correlated with an increase in cerebellar crowding in the caudal CCF. It should
be noted that small breed dogs and Labradors do not show the same relationship.
We infer from this result that during cranial development in Labradors and small
breed dogs, a compensatory mechanism maintains the relationship between
cerebellar volume and CCF dimensions, and this mechanism is defective in CKCS."
(e) "We also found in CKCS that cerebellar crowding in the
caudal CCF is more sensitive to changes in relative cerebellar volume than
cerebellar crowding in the rostral CCF, which is consistent with the theory that
increased cerebellar volume results in the cerebellum shifting caudally and
causes obliteration of dead space in the caudal CCF. This also causes herniation
of the cerebellum through the foramen magnum (i.e. CM)."
(f) "In this study, we find that in CKCS, unlike small breed
dogs or Labradors, there is a positive correlation between the volume of the
cerebellum and degree of crowding in the caudal CCF, which suggests that CM may
be due to CCF development not keeping pace with growth of the cerebellum. This
supports the idea that CM/SM in CKCS may in fact be multifactorial and an
abnormal development process affecting the CCF may be acting as a disease
modifier."
(g) "Impaired CCF development may be caused by a failure of
communication between one or more of these progenitors and the developing neural
tube (specifically, rhombomere 1, which gives rise to the cerebellum).
Alternatively, it could simply be explained by premature closure of growth
plates between the bones of the CCF."
(h) "It has also been noted on post-mortem examination of
CKCS and other small breed dogs that the supraoccipital bone overlying the
cerebellar vermis is remarkably thin and sometimes eroded so that the foramen
magnum is enlarged dorsally, which could indicate that there has been
substantial bone resorbtion. Work is needed to elucidate the mechanisms of
occipital growth in dogs to determine the extent to which an osteoresorbtive
process can mitigate an enlarged cerebellum in CKCS and in other breeds."
However, in a
June 2012 article
German researchers Martin J. Schmidt, Martin Kramer, and
Nele Ondreka compared the volumes of occipital bones of cavaliers with
and without syringomyelia and of French bulldogs. They did not find a reduced
volume of the occipital bone of CKCSs, compared to the bulldogs. They concluded:
"These results do not support occipital hypoplasia as a cause
for syringomyelia development, challenging the paraxial mesoderm insufficiency
theory. This also suggests that the term Chiari-like malformation, a term
derived from human studies, is not appropriate in the Cavalier King Charles
spaniel."
The authors of this 2012 German article seemed mired in
the pre-2010 definition
of Chiari-like malformation. They state:
"... [T]he Chiari-like malformation in the Cavalier King
Charles spaniel is characterized by indentation of the occipital (bone) with
cerebellar herniation and is more correctly termed caudal occipital malformation
syndrome."
They also appear to be unduly dismissive of the studies beginning in 2009
which found that the cavalier's cerebellum is relatively larger than that in
other breeds. The authors of the 2012 German article did not include cerebellum
size in their study, and their comment about the 2009-2012 reports simply is:
"Results of studies proposing a mismatch between cerebellar
and caudal cranial fossa volume in this breed and in comparison to other breeds
were controversial
. In some studies, there was a mismatch between
caudal fossa parenchyma and caudal fossa volume in dogs with syringomyelia and
overcrowding was proposed as a cause of syringomyelia development. In most
studies, however, no difference was found between caudal fossa volume in
Cavalier King Charles spaniels with and without syringomyelia, although this was
not universal." (Emphasis added.)
In a
February 2013 report
, UK researchers T. A. Shaw, I. M. McGonnell,
C. J. Driver, C. Rusbridge, and H. A. Volk
compared MRI scans of 45 CKCSs, 38 dogs of other small breeds, and 26
Labrador retrievers, and concluded:
"The data support the hypothesis that CM/SM in CKCS is a multifactorial
disease process governed by the effects of increased hindbrain volume and
impaired occipital bone development. The present authors recently reported
that CM/SM is linked to increased cerebellar volume (Shaw and others 2012).
In view of this, the aetiopathogenesis of CM/SM may equivocally be mediated
by conditions independently affecting the developing occipital bones and
cerebellum, or by dysregulation of a signaling mechanism coordinating the
growth of the developing hindbrain and occipital skull."
In a
June 2013
report
, UK and German neurology researchers Joe Fenn, Martin J.
Schmidt, Harriet Simpson, Colin J. Driver, and Holger A.
Volk, having compared 22 cavaliers with SM and 12 without SM, found
that in CKCSs with SM the percentage of space taken by venous sinuses in the
brain is significantly lower than the volume occupied by the brain's
parenchyma. Venous sinuses are a network of channels in the brain, which
receive blood from the brains veins and also receive cerebrospinal fluid
(CSF) and empty blood into the jugular vein.
The report concludes that: "These results support a role for reduced venous
drainage and parenchymal 'overcrowding' of the CCF [caudal cranial fossa]
in the pathophysiology of SM."
In a
2013 doctorate dissertation
, German Dr. Melanie Klinger
studied the cranial base growth plates of 58 cavaliers and 24 other
brachycephalic dogs and 67 mesocephalic dogs for the their first 18 months.
She found that:
"In the CKCS the growth plate closure occurred about the 5th month of life.
The second group which was composed of the brachycephalic participants of
the study followed next. Finally the synchondrosis sphenooccipitalis
ossificated in representatives of mesocephalic breeds around the 13.5th
month."
She concluded:
"The results confirm the assumption that the premature ossification of the
sphenooccipital synchondrosis is the cause of the reduced skull length for
brachycephalic breeds. ... With regard to the pathogenesis of the CM the
present results support the exceptional position which the CKCS possesses
among the brachycephalic breeds."
See also
this June 2013 article
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Other factors leading to SM
The severity of CM in a dog does not predict the presence of
syringomyelia in that dog.  Therefore, other factors are believed to
influence the development of a syrinx, including
atlanto-occipital overlapping (AOO)
Ongoing research into genetic
correlations between CM and SM seeks to determine whether different genes
may control the expression of SM and CM.  If so, it may be possible to
select breeding stock which has been diagnosed to have CM but may not be
expected to produce offspring with SM genes.
• Atlanto-Occipital Overlap
(AOO)
The atlas is the spinal
vertebra (C1) closest to the skull. It sits next to the foramen magnum, the
hole in the occipital bone. The "atlanto-occipital joint" is the
connection between the atlas and the occipital bone, and is stabilized
by ligaments. "Atlantooccipital overlapping" (AOO) is characterized by a
decreased distance between the atlas and the occipital bone. In some
cases, the dorsal arch of the atlas may actually protrude into the
foramen magnum. See the
image below
(courtesy of: www.wikispaces.com).
In a
February 2014 article
, a leading neurology team studying the
Griffon Bruxellois observed:
"In other words a developmental anomaly resulting in a Chiari
malformation may also be associated with abnormalities of the atlas,
axis and dens. In the dog, the most important craniovertebral junction
abnormality associated with CM is atlanto-occipital overlapping, which
has been reported as similar to basilar invagination in humans."
In a
January 2016
article
, Cornell University
neuroglogists examined the
MRIs of 271 dogs, measuring the proximity of the atlas to the foramen
magnum. They found a close association (higher than previously reported)
between atlanto-occipital overlapping (AOO) and small breed dogs,
including cavalier King Charles spaniels, affected with clinical signs
of syringomyelia (SM).
See also these related articles:
May 2009
October 2009
January 2010
April
2013
November 2015
May 2016
; and
June 2016
RETURN TO TOP
Pain due to CM
See
Pain due to CM
under
Symptoms
below ...
RETURN TO TOP
Syringomyelia (SM)
introduction to SM
terminology of SM
definitions of SM
what SM is
ole of the ventricle system
other causes of SM
For a thorough, current review of research into syringomyelia and its
diagnosis and treatment, read Dr. Clare Rusbridge's
June 2020 article, "New considerations about Chiari-like malformation,
syringomyelia and their management", linked here
Also, See also,
these
YouTube videos by Dr. Rusbridge
that fully explain what
syringomyelia is in the cavalier.
Introduction to SM
Syringomyelia
(SM) is a condition of the development of
fluid-filled cavities in the spinal cord, which is the consequence of the
shortening of the skull base --due to
brachycephaly
-- and additional changes around the first vertebra,
which result in over-crowding at the junction of the brain and the
spinal cord -- the foramen magnum -- obstructing the normal free flow of
cerebrospinal fluid (CSF) between the hind end of the brain and the
spinal cord. The CSF is forced through the foramen magnum at high
pressures into the spinal cord, creating the cavities in the cord.
"Syringomyelia" is Latin for "cavity within the spinal cord".
In the cavalier King Charles spaniel, SM is considered secondary to
Canine Chiari Malformation (CM).
SM was first identified by veterinary neurologists in the 1990s,
while classic symptoms, such as air scratching, had been reported anecdotally
in the 1980s.
The severity and extent of syringomyelia also appear to
get worse in each succeeding generation of cavaliers. Other breeds known to
be affected to a lesser extent include the
Affenpinscher,Bichon Frise, Boston terrier,
bull terrier, French
bulldog, Havanese, King Charles spaniel (the English toy spaniel), Maltese
terrier, miniature dachshunds, miniature and toy poodles, Papillon,
Pomeranian, Pugs, Shih Tzu, Staffordshire bull terrier, and the Yorkshire
terrier.  See
SM in Other Breeds, below
for links to Internet articles about syringomyelia in some of these breeds.
Courtesy of The Dog Channel
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Terminology of SM
Syringomyelia is also known as syrinx and hydromyelia, and occasionally mis-identified
as Arnold Chiari malformation.
"Syringomyelia" is Latin for "cavity within the spinal cord".
Technically, hydromyelia is a dilatation of the central canal
within the spinal cord, and syringomyelia is the cavitation of the spinal
cord parenchyma.  Combined, they are referred to either as
syringohydromyelia (SHM) or hydro-syringomyelia.  The disease is
referred to generally as syringomyelia and SM herein.  This condition
is similar, but not identical, to Arnold Chiari Type I Syndrome in humans.
Syringomyelia also may be described as syringomyelia secondary to canine Chiari
malformation (CM).
CM is also referred to as occipital hypoplasia (OH) or caudal occipital malformation syndrome (COMS).
The full relationship between CM and the development of SM is not fully
understood. The combination of CM and SM usually is abbreviated as CM/SM.
In a
2020 article
, Dr. Clare Rusbridge has explained the changes in
definitions and terminology of SM over the past two decades, as follows:
"The
nomenclature of SM has morphed over the years since the first
description in the early 19th century. Authoritative sources use SM
rather than historical terms syringohydromyelia, hydrosyringomyelia or
hydromyelia. This is because the anatomical distinction between these
terms is theoretical rather than a reality (Rusbridge and Flint 2014).
It is conventional in veterinary medicine to refer to a central syrinx,
less than 2 mm in transverse diameter, as a central canal dilation (Fig
3), even though the ependymal lining of the central canal is disrupted
with only minor dilation (Radojicic and others 2007). Non-inflammatory
spinal cord oedema, as distinct from cavities containing free fluid, is
referred to as presyrinx (presyringomyelia). Presyrinx most commonly
affects the dorsal and ventral columns of the spinal cord and may
eventually progress to SM (Fig 3). The oedema can reverse if the cause
can be addressed. CNS inflammatory diseases can also cause spinal cord
oedema and are alternative differentials for spinal cord oedema (Fig
4)."
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Definitions
of SM
Syringomyelia (SM) is defined as "a condition that results in the
development of fluid-containing cavities within the parenchyma of the spinal
cord. as a consequence of abnormal cerebrospinal fluid movement." (November
2006 International Conference on Syringomyelia).
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What SM is
Cerebrospinal fluid (CSF) surrounds the spinal cord and the brain.
The brain and spinal cord literally are suspended within the CSF, which
serves to insulate them from injury as they float within it. The fluid
is contained in a three layered membrane called the
meninges
CSF normally flows back and forth between the brain and
spinal cord with each heart beat.  As the heart pumps blood to the
brain, the CSF flows from the brain through the hole called the
foramen
magnum
to the spinal cord, to accommodate the increased volume of incoming
blood.
Syringomyelia is believed to result when the cerebrospinal fluid is prevented from
circulating normally between the brain and spinal cord, due to a narrowing
or blockage of the CSF flow at the foramen magnum, thereby forcing the CSF
at a higher than normal pressure into the spinal cord. called spinal cord
cavitation.  The pressure
difference causes the spinal cord to distend or pull apart, creating a
cavity called a syrinx, and squeezing fluid either from blood vessels and other
tissues or CSF into the
cavity. Once a syrinx is created, as the CSF moves through the spinal cord
in each direction, the syrinx fills with CSF and then empties repeatedly.
(See above a magnetic resonance imaging [MRI] scan of a
cavalier's brain and spinal cord, with the arrow
pointing to a syrinx [the
elongated white area] within the spinal cord. The blue and gray diagram
at right -- prepared by Dr. Rusbridge -- shows the location of the syrinx
within the spinal cord. In the images of a cavalier
below, the red arrow points from a syrinx to a cross-section of the spine at
that point.
This image is Figure 3 from this
November 2018 article
.)
However, in a
September 2015
abstract
before the ESVN-ECVN, UK researchers created a computer model of the spinal
cord, subarachnoid space (SAS), dura mater, and the epidural space of a
cavalier King Charles spaniel affected with CM/SM. They performed
exaggerated movement of the spinal cord during the cardiac cycle,
seeking to confirm a theory that abnormities in the circulation of the
cerebrospinal fluid (CSF) generate pressures that drive the fluid into
the cord. Instead, they found that CSF pressure gradients are unlikely
to cause fluid movement into the cord, sufficient to generate syrinxes.
They concluded:
"On the other hand, although the shear stress in the cord is low, its
location and cyclic nature indicates the possibility that this may be
the factor that generates the initial tissue damage, which eventually
leads to the formation of syrinxes."
Syringomyelia is an extremely serious, progressively worsening spinal
disease which is rare in most breeds but is becoming very widespread in
cavalier King Charles spaniels of all bloodlines.  In May 2005,
Dr. Rusbridge
and Susan P. (Penny) Knowler, BSc (Hons),
who have been studying the disease in several hundreds of cavaliers,
reported that a conservative estimate is that at least 50% of cavalier King
Charles spaniels have a degree of Chiari-like malformation, although not all
are so severely affected as to have syringomyelia. In February 2010,
Dr. Georgina Child,
board certified veterinary neurologist in
Australia, reported that of 60 asymptomatic cavaliers scanned as potential
breeding stock, 50% had SM syrinxes. In a
September 2010
report
of 804 cavaliers, Mrs. Knowler and others estimated that "the
lifetime risk of developing syringomyelia in the study population was
estimated to be 55%."
In a
2011 study
of 49 cavaliers diagnosed with SM, Dr. Rusbridge and others found that
"total syrinx size was positively correlated with age" of the dogs. In a
June 2011 study
of 555
cavaliers without any symptoms of syringomyelia, 25% of the one year old
dogs had SM and 70% of the dogs aged 6 years and older had SM.
In an
October 2021 article
, Drs. Srdjan Cirovic and Clare Rusbridge report
on a computer model they devised
which may explain how SM syrinxes (syringes) are created and expand, due to the impulsive movement of
cerebrospinal fluid (CSF), called "slosh". A magnetic resonance imaging
(MRI) scan of a cavalier was used as the model
design for the study. The investigators conducted simulations of various
spinal cord conditions, from the cord being free of cavities to small
syringes at different locations to a prorgessively expanding syrinx.
(See Figure 2.)
They found that, if small syringes are present, there are peaks of
stress at those locations, the effect being most pronounced at the
locations at which syringes initially form. When the syrinx reaches the
lumbar region, the stress becomes moderate. They concluded that their
findings support the "slosh" hypothesis, suggesting that small cervical
syringes may progress, but when the syrinx is large, there is less
stress, which may explain why a syrinx can rapidly expand but then
remain unchanged in shape over years. Their stated conclusions:
"The results of this study strongly suggest that the spinal cord
tissue in the vicinity of fluid-filled cavities experiences higher than
normal mechanical stress due to the movement of the CSF from epidural
excitation. When the syringes are longer than approximately 30 mm,
filling of the epidural veins may generate the "slosh" effect, where the
fluid is forced to the caudal end of the syrinx. The results for the
simulations of an expanding syrinx are broadly consistent with the
homeostatic hypothesis, as the stress in the cord is lower for the fully
developed syrinx than for smaller syringes. Other, potentially more
realistic, scenarios for syrinx expansion should be examined in the
future. This study specifically addresses syringomyelia in dogs, and
more specifically in CKCS. ... Considering anatomical and other
differences (e.g., upright posture in humans) the results regarding the
potential pattern of syrinx enlargement do not apply to humans or to dog
breeds other than CKCS."
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ole of the ventricle system
(ventricular dilatation - ventriculomegaly)
The brain's ventricle system consists of
four cavities which are connected with the spinal cord's central canal. The
four ventricles are known as the two lateral ventricles, the third
ventricle, and the fourth ventricle. The ventricles are the source of CSF
and are the brain's respository of CSF.
Some neurologists are including in their examination
reports an analysis of whether the ventricles are dilated, and if so, a
measurement of the amount of their dilatation. The medical term for dilated
lateral ventricles is
ventriculomegaly
(See our
ventriculomegaly webpage
for more
information about this disorder.)
In a
December 2010 UK study
led
by Dr. Colin Driver, , the researchers' results were consistent with
the previous findings that ventriculomegaly and a small but significant
increase in caudal fossa parenchyma are associated with syringomyelia.
In an
October 2016 abstract
, German researchers compared the perfusion of
blood in the periventricular white matter of 23 cavalier King Charles
spaniels with ventriculomegaly compared to control dogs consisting of 10
healthy Beagles. They found that cerebral blood flow and volume were
significantly lower in the cavaliers. They concluded that the dogs with
ventriculomegaly may have a form of normal pressure hydrocephalus (NPH).
In an
August 2017 article
, the same German team studied the ventricle
system of 42 cavaliers -- 32 CKSCs with ventriculomegaly and 10 control
CKCSs. They used "dynamic susceptibility contrast perfusion" magnetic
resonance imaging (DSC-PMRI), which allows them to quantify the volume
of blood passing through the brain tissue. They found that cerebral
blood flow (CBF) is reduced in the periventricular white matter of CKCSs
with ventriculomegaly, which makes some increase of intraventricular
pressure likely. They stated that these findings make it plausible that
ventriculomegaly may be a form of internal hydrocephalus. They observed
that when intraventricular pressure is increased, a higher cerebrospinal
fluid (CSF) volume is forced from the ventricles at a higher velocity.
In a
July 2022 article
, Italian researchers reviewed the clinical records of 43 cavaliers diagnosed with CM, to to calculate
the sizes of their lateral ventricles and determine if there is any the
association between ventriculomegaly and clinical signs, ventricular asymmetry, grade of CM, SM, and degree of medullary kinking. The most common initial
clinical signs were scratching and neck pain. Ventriculomegaly was
identified in 70% of dogs, CM grade 2 (CM2) was
observed in 77% of cases, ventricular asymmetry in 54% and SM in 80% of the
cavaliers. The median medullary kinking index was 37.77%, and 28% of the
dogs had epileptic seizures. They report finding:
• No significant association between the grade of SM and class of
ventriculomegaly.
• No significant association between dimension of
lateral ventricles and any other conditions.
• No significant
association between medullary kinking index and class of
ventriculomegaly.
• No significant association between primary
secretory otitis media (PSOM) and any clinical signs.
They concluded that "the prevalence of ventriculomegaly in Cavalier
King Charles Spaniels is high but this finding does not seem related to
the severity of clinical signs, presence of Chiari-like malformation,
syringomyelia and craniocervical junction abnormalities such as
medullary kinking.
Below is a comparison between a canine brain with normal lateral
cerebral ventricles (A) and one with enlarged lateral ventricles (B).
From a
May 2015 study
led by Dr. Martin J. Schmidt.
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Other causes of SM
There are other forms of syringomyelia in canines. Spinal dysraphism or
spinal dysplasia is a genetic disorder in which puppies normally under the age
of three months display a bunny hopping gait and wide-based stance and
scoliosis, due to the spinal cord not developing completely in the womb.
Dalmatians, English setters, golden retrievers, rottweilers, visla, and
Weimaraners have been identified with this disorder. Also, SM may be caused by
tumors, cysts, or trauma. Neither of those are discussed here.
Also, benign, small syrinxes are a common incidental finding on MRI
examinations. Therefore, clinical
correlation is important in order
to determine if the syrinx is associated with the Chiari-like
malformation and/or symptoms.
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Symptoms
Symptoms due to CM
Symptoms due to SM
The following paragraphs discuss typical symptoms (clinical and
behavioral signs) displayed by dogs diagnosed with Chiari-like
malformation (CM) and/or syringomyelia (SM). CM and SM each cause
different symptoms. Most signs of CM are due to pain. SM also can cause
pain, but usually only late in the progression or in the most severe
cases.  The most common symptom of SM is
phantom
scratching
. For more information about pain due to CM and SM, see
Expressions of Pain
, below.
Several of these signs are so common that they may be for other
reasons and unrelated to CM or SM at all. For example, prior studies
have shown that approximately 25%  of dogs that display clinical
signs of SM are not found to have a syrinx on MRI scans. Scroll down to
"Other disorders with
similar symptoms"
for a discussion of likely other disorders causing
similar signs.
SM and CM very seldom can be detected in young puppies, as
symptoms usually are not evident before the age of six months or even many
years later. There is no way to know in advance of the symptoms whether a
dog is normal or is a syringomyelia carrier which does not develop the
disease but can pass it on to its offspring.
NOTE: Veterinarians will tell us that dogs do not have "symptoms"
but instead have "signs". But, for us laymen, the word "signs" can be
confusing because of its different meanings. So, for us, "symptoms" it
is.)
Symptoms due to CM
The most common symptoms of Chiari-like malformation (CM) are
the result of feeling head aching pain, such as grimacing facial
expressions (pain face) and squinting at bright lights (photophobia).
Other indications include:
• Vocalization in 65% of cavaliers diagnosed with CM: Yelping or
moaning when
the dog changes its position, or when being lifted up, or while asleep,
or seemingly at random.
• Head (especially at the back of the head) and ear scratching or rubbing the face on surfaces, in 28% of
cavaliers diagnosed with CM. See
Dr. Clare Rusbridge's short YouTube video
demonstrating this type of
scratching and rubbing.
This section discusses typical symptoms (clinical and behavioral
signs) displayed by dogs diagnosed with CM. Most signs of CM are due to
pain. SM
also can cause pain, but usually only late in the progression or in the
most severe cases. (
See "Pain Due to SM",
below.
Symptoms, signs, and behaviors which
may
be
due to CM include:
• Expressions of pain,
discussed
below
• Temderness at the neck, shoulders, and/or head
• Head shaking
(CM or SM)
Lip licking
• Head rubbing -- side to side on the floor
• Reduced physical activity (CM or SM)
• Behavioral change to more timid, anxious, or aggressive
• Touch aversion
(CM of SM)
• Inability to lower head to eat or drink (CM or SM)
• Restlessness -- inability to settle down
• Sleep disorders
It also is possible that a dog with CM does not have SM but still may have symptoms of SM due to the CM
obstructing the flow of cerebrospinal fluid (CSF). This also is attributed
to a direct compression of the medulla oblongata, which is involved in the
modulation of pain.
In a
November 2018 article
, Drs. Rusbridge and Knowler summarize how
to diagnose pain due to CM as follows:
"Diagnosis of CM-pain is made by appropriate clinical signs in
addition to MRI brain findings of a brachycephaly with rostrotentorial
crowding including rostral flattening, olfactory bulb reduction and
rotation, increased height of the cranium with reduction of the
functional caudotentorial space and hindbrain herniation. There may also
be changes suggesting raised intracranial pressure such as loss of sulci
definition with ventriculomegaly. The cisterna magna is reduced."
In
an October 2012 study
by UK researchers of 48 cavaliers, nine of which had
only CM and the rest also had SM, neuropathic pain progressed in 75% of the dogs
over a mean average period of 39 months. The researchers noted that it is not
fully understood how CM/SM causes neuropathic pain, and they did not make any
such finding. However, their report confirms that neuropathic pain does exist,
and it progresses, in cavaliers with only CM.
In a
January 2017 article
, UK researchers determined, from its group of
28 cavaliers with pain due to CM but not SM, that they "had a short
basicranium (line
ab
in Figure 1 below) with a resultant
compensatory increased cranial height (small
angle 7
, below)
and increased brachycephaly with olfactory bulb more ventrally rotated
(p = 0.003) and rostral forebrain flattening compared to Control CKCS.
However, in comparison with SM dogs, the CM cohort has a longer line
bc
and a wider
angle 9
increases the volume of the caudal
fossa, which may lessen obstruction to CSF flow and the risk of
developing SM."
In a
November 2017 article
a team of researchers at NC State University and Cornell University prepared and studied the
results of a questionnaire answered by owners of 50 cavalier King
Charles spaniels, 20 with only Chiari-like malformation (CM) and 30 with
both CM and syringomyelia (SM). Of the 50 dogs, 33 were symptomatic and
17 were not. The most common presenting sign was phantom scratching,
occurring in 32 dogs, and the most common sign of pain was crying out
when being lifted, occurring in 11 dogs. The researchers found that
owner-reported findings were not significantly associated with presence
or severity of SM or neurologic examination findings. Ten of the 20
CM-only dogs reportedly displayed "classic" signs of neuropathic pain.
The series of questionnaires are linked here:
Preliminary
Questionnaire
--
Dog Diagram
(ChiMPS-M)
--
Final Questionnaire
(ChiMPS-T)
. The researchers
concluded:
"T" The conclusion that SM causes pain in CKCS is complicated by the
finding that dogs with CM but no SM can show classic signs of
neuropathic pain, as illustrated by 10 dogs in our study. ... To
conclude, the full range of signs reported by owners of CKCS includes a
variety of manifestations of pain, with phantom scratching as the most
commonly reported sign followed by crying out when being lifted. Owner
reporting of pain and scratch frequency and severity captured by the
ChiMPS-T correlates with the owner-reported surface area affected by
these signs in their dogs. Neither the scores nor the surface area
reported correlated with the presence or severity of SM, highlighting
uncertainty on the source of pain in these dogs."
In Figure 8 below, this comparison series of MRI scans of three
cavaliers (from this November 2018 article by Drs. Rusbridge and
Knowler) demonstrates differences in the positioning (and crowding) of
the brain among dogs with normal, CM-pain-affected, and SM-affected
conditions. See, also, our discussion of
Syringomyelia -- Expressions of Pain
, below.
In a
July 2019 article
, UK neurology researchers studied the
records of 130 cavalier King Charles spaniels diagnosed with CM and some also with SM to determine
which symptoms (clinical and behavioral signs) related to CM and to SM
and to syrinx diameter, in order to use the data in future studies of
diagnosis, treatment, and genetics of CM/SM. Dogs were grouped based
upon whether they had no SM (Group 1) up to having a syrinx greater than
4 mm (Group 4).
igns found NOT RELATED to syrinx presence or size:
Vocalization (65.4%) (except being picked up under the sternum
(breastbone), which was more common among dogs with no or mild SM).
•  Spinal pain -- 54.6%
•  Reduced activity -- 37.7%
•  Reluctance to
jump or to climb stairs --35.4%
•  Aversion to touch or grooming --
30.0% (ears, head, and neck region -- 25.4%)
•  Change in emotional
state (more timid, anxious, withdrawn, or aggressive) -- 28.5%
Disrupted sleep -- 22.3%
The implication from this study is that the major signs
of pain expressed by CM/SM cavaliers definitely are not due to having a
syrinx and probably are due to having Chiari-like malformation, but the
authors cannot definitely attribute the painful expressions solely to
CM.
As the disorder progresses, there usually follows increasingly severe
pain around the dog's head, neck, and shoulders, causing it yelp or scream.
This is described as "vocalization" -- spontaneous, when picked up under the
sternum, or when changing position especially at night.
It is believed to be a neuropathic pain, probably due to disordered neural
processing in the damaged dorsal horn.
(Photos at right
are of a cavalier both without pain and then
suffering severe head pain due to CM. Courtesy of
Dr. Clare Rusbridge, Fitzpatrick Referrals, UK.)
In a
May 2014 report
, USA researchers assessed 36 cavalier King Charles spaniels for neurologic pain
and dysfunction. They found that 20 of the dogs demonstrated neuropathic
pain; that dural bands (compressive lesions caused by abnormally
thickened dura mater
at the craniocervical junction) were present in 31
of the dogs; that 34 of the dogs had Chiari-like malformation; that 23
of the dogs had syringomyelia (and 21 of those 23 dogs had dural bands).
They also found that dural bands were associated with both the presence
and severity of clinical signs and the presence of SM, and that higher
compression indices were associated with more severe SM. They concluded
that:
"Dural bands appear to play a significant clinical role.
Compression indices provide a better assessment of dural band severity
compared to grading."
Dura mater is is a
thick membrane made of dense tissue that surrounds the brain and spinal
cord. It is the outermost of the three layers of membrane called the
meninges that is directly inside the skull bone.
Similar forms of neuropathic pain in humans suffering from Chiari type I
malformation (the human counterpart to CM and SM include: (a) a burning type
pain, pins-and-needles and other odd sensations (called dysaesthesia); (b) pain
from a stimulus which is not normally painful, such as light touch or motion
(called allodynia); (c) increased pain from stimuli which are normally painful
(called hyperpathia,); and (d) a constant, burning type pain (called causalgia).
In humans, neuropathic pain also is associated with anxiety, depression, and
reduced quality of life.
In a
January 2025 YouTube video
, Dr. Clare Rusbridge observed that as
CM-affected cavaliers grow older, their brains shrink, and as a
consequence, the severity of fhe CM -- and thus the resulting pain --
may reduce.
RETURN TO TOP
Symptoms due to SM
Phantom scratching
Other common symptoms
Expressions of pain
Changes in barometric
pressure
Other disorders
with similar symptoms
ymptoms not due to CM/SM
The most common symptom of syringomyelia (SM) is
phantom scratching
. In 48% of
cavaliers diagnosed with SM, they display rhytmic scratching with a rear
leg, where the foot scratches at empty air, usually when the dog is
being walked on a leash. See
Dr. Clare Rusbridge's short YouTube video
demonstrating this type of
scratching.
The following paragraphs discuss typical symptoms (clinical and
behavioral signs) displayed by
dogs diagnosed with SM.
CM and SM each cause different symptoms. Most signs of CM are due to
pain. (
See "Pain Due To CM", below.
) SM
also can cause pain, but usually only late in the progression or in the
most severe cases. (
See "Pain Due to SM",
below.
Several of these signs are so common that they may be for other
reasons and unrelated to CM or SM at all. For example, prior studies
have shown that approximately 25%  of dogs that display clinical
signs of SM are not found to have a syrinx on MRI scans. Scroll down to
"Other disorders with
similar symptoms"
for a discussion of likely other disorders causing
similar signs.
Phantom scratching
What it is
What it is not
Dorsal horn damage as
cause
Prior research into causes
Symptoms
of CM and SM
may vary widely among different dogs, but the most common sign of SM (and
not of CM) often is that
the dog feels a sensitivity in its neck area, causing in some an
uncontrollable urge to scratch at its neck and shoulders excessively,
particularly when walking or during other forms of exercise, and usually
without making skin contact. It also can be prompted by rubbing certain
areas (
see dermatome, below
) of the
skin.  This is called
phantom scratching
or
fictive scratching
or
maladaptive scratching.
See the description of phantom scratching by Dr. Clare Rusbridge in her
YouTube video linked here
• What it is not
Phantom scratching is specifically limited towards the neck area and
in most all cases, only on one side. Chronic scratching in other areas is not the phantom
scratching associated with SM. For example, dogs with CM may scratch at
the back of their head or their ears due to head pain. In general, head
or ear scratching, or being itchy all over the body, is not phantom
scratching nor is it related to CM.
(Photo at right is courtesy of
Passionate Productions.)
See also, the description of phantom
scratching by Dr. Clare Rusbridge in her
YouTube video linked here
In a
July 2019 article
, a team of UK neurology researchers  studied the
records of 130 cavalier King Charles spaniels diagnosed with CM and some also with SM to determine
which symptoms related to CM and to SM
and to syrinx diameter, in order to use the data in future studies of
diagnosis, treatment, and genetics of CM/SM. Dogs were grouped based
upon whether they had no SM (Group 1) up to having a syrinx greater than
4 mm (Group 4).
Signs found NOT RELATED to syrinx presence or size:
Vocalization (65.4%) (except being picked up under the sternum
(breastbone), which was more common among dogs with no or mild SM).
•  Spinal pain -- 54.6%
•  Reduced activity -- 37.7%
•  Reluctance to
jump or to climb stairs --35.4%
•  Aversion to touch or grooming --
30.0% (ears, head, and neck region -- 25.4%)
•  Change in emotional
state (more timid, anxious, withdrawn, or aggressive) -- 28.5%
Disrupted sleep -- 22.3%
Signs found TO BE RELATED to syrinx
presence or size:
•  Phantom scratching -- 67% of Group 4 dogs and
none in other groups
•  Scratching or rubbing of the head or ears -- 28%
but less common in Group 4 dogs
•  Scoliosis -- 27% of Group 4 dogs and
none in other groups
•  Postural defects -- 15% of Group 4 dogs and none
in other groups
•  Weakness -- 39% of Group 4 dogs and none in other
groups
The researchers stated that their findings suggest that "phantom
scratching is highly unlikely with small syrinxes." They also found that
among the dogs in their study,
PSOM (primary secretory otitis media)
is
common in symptomatic CM-affected dogs and in SM-affected dogs, thereby
raising the possibility of confusing the cause of some signs and
behaviors, since PSOM-affected dogs tend to engage in ear-rubbing. They
concluded:
"The study further suggests that SM-specific signs are phantom
scratching, scoliosis, and sensory and motor signs that can be related
to spinal cord damage by the syrinx and are associated with large
syringes (transverse width >4 mm). Non-SM-specific signs include
vocalization (described as without obvious trigger, when shifting
position when recumbent and when being lifted under the sternum to a
height), spinal pain, head and ear rubbing or scratching, aversion to
touch, refusal or difficulty jumping or doing stairs, exercise
intolerance/reduced activity, sleep disruption, or behavioral change
described as becoming more anxious, timid, aggressive, or withdrawn.
These non-SM-specific signs could reflect CM-P [CM associated pain]."
The implication from this study is, therefore, that the major signs
of pain expressed by CM/SM cavaliers definitely are not due to having a
syrinx and probably are due to having Chiari-like malformation, but the
authors cannot definitely attribute the painful expressions solely to
CM.
• Dorsal horn damage as cause
In Dr. Rusbridge's
January 2024 YouTube video
on phantom scratching, she states that
being able to prompt or evoke phantom scratching by rubbing an area of
the dog's skin indicates that there is dorsal horn damage caused by a
syrnix. The specific area of the skin is a
dermatome
which is an area of skin receiving sensory innervation from a single
spinal nerve dorsal root. The location of the syrinx causing damage to
the dorsal horn is at the C2-C4 vertebrae, particularly if the syrinx
wide and is asymmetrical and extends up to the dorsal nerve root entry
zone. Occasionally a syrnix in the cranial thoracic region will cause
scratching near the sternum (breastbone).
Dorsal horns
are two projections from the rear of the spinal column
which contain neurons and cells of the central nervous system.
(See
diagram at right. They are at the outer tips at the 2 o'clock and 10
o'clock locations.)
Each of the two horns consists of layers of gray
matter called "
laminae
", which are divided into sections (laminae I
through VI in the dorsal horn) based upon their location and function.
In a
March 2022 article
, Danish researchers studied eight cavaliers
diagnosed with SM and four others without SM, to determine if phantom
scratching on only one side of the body of SM-affected dogs related to
pathological changes in their spinal cords. Seven of the eight
SM-affected CKCSs displayed signs of pain by phantom scratching on only
one side of their bodies, called "
unilateral scratching
". They examined
the two dorsal horns in spinal cord segments C1 through C8 specifically.
The investigators reported finding that the cavaliers which phantom
scratched on only one side had some loss of the volume of laminae I
through III of the dorsal horn which is located on the same side of the
spinal cord as the side the dog phantom scratches, compared to the
dorsal horn on the opposite side. They also noted that in cavaliers
which unilaterally scratched, there were changes in the pain pathways at
the dorsal root entry zone of those dogs.
• Prior research into causes
Phantom scratching previously had been believed to
be due to an increase in the pressure of the flow of cerebrospinal fluid
through the central canal from the brain down the spinal column, causing the
central canal to expand and press against the nerves of the spinal column
and creating a pins-and-needle-like tingling or a burning-type pain, and
other strange sensations (called dysaesthesia or paresthesia), which prompt the dog to scratch.
However, in a
May 2016 abstract
, UK researchers fou nd that phantom scratching is
associated with a very wide syrinx -- 4 mm. wide or greater in cavaliers -- that extends to the superficial dorsal horn (SDH)
in the C3-C6 spinal segments. The study found that phantom scratching is
associated with a large dorso-lateral syrinx
that extends to the SDH in the
C3-C6 spinal segments (C2-C5 vertebrae). The study did not find an association
to damage of other areas of cervical spinal cord. They suggested that phantom
scratching is due to damage to projection neurons in lamina I of the superficial
dorsal horn (SDH) with resulting reduced descending inhibition to the
lumbosacral scratching CPG [central pattern generator -- neural circuits
controlling a stereotyped sequence of muscle contractions]. ... They concluded
that if a dog has an SM syrinx extending to the SDH then it is at risk for
phantom scratching. In a
November 2017 article
-- an extended publication of the
May 2016
abstract
-- the same investigators concluded:
"SM associated phantom scratching appears associated with MRI
findings of a large syrinx extending into the mid cervical SDH. We
hypothesise that damage in this region might influence the lumbosacral
scratching central pattern generator (CPG). If a scratching SM affected
dog does not have a large dorsolateral cervical syrinx with SDH
involvement then alternative explanations for scratching should be
investigated."
This article suggests that only dogs with both CM and SM will phantom
scratch, and that dogs with only CM will not. It also suggests that the
action is very similar to fictive scratching which occurs in animals
with severed spinal cords.
In a
November 2017 article
a team of researchers at NC State University and Cornell University prepared and studied the
results of a questionnaire answered by owners of 50 cavalier King
Charles spaniels, 20 with only Chiari-like malformation (CM) and 30 with
both CM and syringomyelia (SM). Of the 50 dogs, 33 were symptomatic and
17 were not. The most common presenting sign was phantom scratching,
occurring in 32 dogs, and the most common sign of pain was crying out
when being lifted, occurring in 11 dogs. The researchers found that
owner-reported findings were not significantly associated with presence
or severity of SM or neurologic examination findings. See Figure 1
(right)
, a chart of the symptoms reported by the owners of the 33
symptomatic dogs.
Ten of the 20
CM-only dogs reportedly displayed "classic" signs of neuropathic pain. The researchers
concluded:
"The conclusion that SM causes pain in CKCS is complicated
by the finding that dogs with CM but no SM can show classic signs of
neuropathic pain, as illustrated by 10 dogs in our study. ... To
conclude, the full range of signs reported by owners of CKCS
includes a variety of manifestations of pain, with phantom
scratching as the most commonly reported sign followed by crying out
when being lifted. Owner reporting of pain and scratch frequency and
severity captured by the ChiMPS-T correlates with the owner-reported
surface area affected by these signs in their dogs. Neither the
scores nor the surface area reported correlated with the presence or
severity of SM, highlighting uncertainty on the source of pain in
these dogs."
RETURN TO TOP
Other common symptoms
of SM
Some dogs perform facial or head rubbing or spontaneous vocalizations.
Click here
or the YouTube logo
(right)
to see videos of cavaliers with SM
symptoms. Videos also are available under
Related Links
below.
Symptoms, signs, and behaviors which
may
be
due to SM include:
Phantom scratching,
discussed above
• Scratching of both sides of the neck and
shoulders
• Aversion to being touched to the head, neck, or shoulders
Worsening of clinical signe when the dog was emotionally aroused
Preferred head posture during sleep
• Pain, usually late in the
progression or in the most severe cases. (
See "Pain Due to SM",
below.
• Head shaking
• Feet licking or chewing -- excessive
• Reduced physical
activity
• Inability to lower head to eat or drink
• Weakness of the hind limbs
• Stiffness of the limbs
Many symptoms of SM, such as scratching, are so ordinary (when not
excessive or compulsive) that they could be attributed to any of several
common causes, including flea bites or allergies. Others, such as limping or
lack of muscle coordination also could be confused with injuries or other
disorders.
Scoliosis
(abnormal curving of the spine) is another physically apparent symptom.
(See photo of a young cavalier with scoliosis, below.
Dr. Rusbridge reports
finding that scoliosis in many SM-affected
dogs will improve slowly over the years.
An outward deviation of an eye, called
exotropia
, also is common among dogs
affected with CM.
SM and CM very seldom can be detected in young puppies, as
symptoms usually are not evident before the age of six months or even many
years later. There is no way to know in advance of the symptoms whether a
dog is normal or is a syringomyelia carrier which does not develop the
disease but can pass it on to its offspring.
SM causes damage to the spinal cord and usually results in
symptoms of hypersensitivity, intense pain, and leg dysfunction. The primary
symptoms may vary widely, and in some cases, a cavalier may even have SM without
displaying any outward symptoms at all.  Some cavaliers
diagnosed with SM lack any clinical signs.  It also is possible that a dog
with CM does not have syringomyelia (the syrinx
in the spinal cord), but still may have symptoms of SM due to the CM
obstructing the flow of cerebrospinal fluid (CSF). This also is attributed
to a direct compression of the medulla oblongata, which is involved in the
modulation of pain.
In the absence of an MRI, the severity of certain SM-related symptoms
and their combinations have been found to indicate the size range of
syrinxes in cavaliers. In a
February 2024 article
, Danish researchers investigated
the symptoms of 89 cavaliers which had been
diagnosed with SM by MRI at the University of
Copenhagen, Denmark. They interviewed the dogs' owners, to determine the
relationship between the sizes of the dogs' syrinxes and their
SM-related symptoms. The severity of the dogs' CM and SM were cagtegorized by the
British Veterinary
Association/Kennel Club scheme
of measuring the condition of the CM and
sizes of the syrinxes. The dogs were distributed into three groups: (1)
dogs with CM and no SM (or with a maximum transverse width < 2 mm), (2)
dogs with CM and small syrinx (SM 2.00-3.99 mm) and (3) dogs with CM and
large syrinx (SM >4 mm). They report finding that these clinical signs
were reported significantly more frequently in dogs with large syrinxes:
• Phantom scratching
• Scratching of both sides of the neck and
shoulders
• Aversion to being touched to the head, neck, or shoulders
Worsening of clinical signe when the dog was emotionally aroused
Preferred head posture during sleep
They found that when phantom scratching, aversion to touch, and a
preferred head posture while asleep were combined, the likelihood of a
large syrinx increased. They concluded that clinicians may use this
information to diagnose CKCSs with a large syrinx and necessary
treatment when MRI diagnosis is not available or affordable.
Ease
the symptoms by using a comfortable harness instead of a collar and
leash. One of the best harnesses for cavaliers with CM/SM symptoms
is the
BRILLIANT K9 "Lucy Small" harness
available on Amazon
It is easy to put on and easy to take off. Watch the videos:
"Opening the harness"
and
"Walking the dog with the harness"
RETURN TO TOP
Expressions of pain
As syringomyelia destroys portions of
the cavalier's spinal cord, the dog may experience so much pain that it may
contort its neck and may even sleep and eat only with its head held high.
Ultimately, the dog may develop scoliosis, as a result.  There may also be
progressive weakness in the legs, so that walking becomes increasingly
difficult. Some dogs deteriorate to the point of paralysis.
In a
June 2007 study
of 55
cavaliers, the researchers reported that the wider the syrinx, the stronger
the predictor of pain, scratching behavior and scoliosis in dogs with
syringomyelia. They stated: "Both pain and syrinx size were positively
correlated with syrinxes located in the dorsal half of the spinal cord."
They also concluded that such pain is likely to be neuropathic pain,
resulting from disordered neural processing in the damaged dorsal horn.
Similarly, in an
August 2012
study
, the researchers found evidence that:
"... the disruption of the dorsal horn structure is a
significant event in the production of clinical signs in CKCS. The spinal cord
dorsal horn in symptomatic CKCS is significantly more asymmetric than that of
control animals, whereas the asymptomatic CKCS have changes that are midway
between control and symptomatic CKCS. This suggests the possibility that
progression from mild to severe asymmetry in CKCS is associated with development
of clinical signs; however such a conclusion cannot be definitively supported by
this study because of the cross sectional nature of the data collected."
Photo is of a cavalier writhing in pain from
CM/SM. Photo is from
Pedigree Dogs Exposed
.)
In a
2009 study
of 64 cavaliers
affected with CM/SM, Drs. Sofia Cerda-Gonzalez, Natasha J. Olby
and others classified clinical signs of pain from grade 0 to grade 5, by which
the dogs displayed symptoms of neck scratching, head scratching, neck pain upon neurolgoical examination, as well as ataxia and paresis detected upon
examination. See table below:
In a
September 2017 study
of CM and SM in Chihuahuas, the researchers used a
questionnaire for the dogs' owners to complete. The questions for dogs included a grading system for the
description of the presence frequency, and severity of CM/SM-related
clinical signs, such as:
1.persistent scratching episodes of the ears or shoulders with or
without skin contact
2.persistent scratching episodes of the cranial
thoracic spine with or without skin contact
3.facial rubbing
4.spinal hyperesthesia
5.vocalization
6.gait incoordination
7.weakness
These were graded from 1 (occurring <2 times a week) to 5 (occurring
several times a day). A percentage from the maximum points (7x5 = 35
points) was calculated for each patient.
In a
2010
Canadian study
, researchers found a significant linear correlation
between the severity of neurologic dysfunction and size of the syrinx, with
a larger syrinx being associated with more severe neurologic signs.
In an
April 2012 study
Geoffrey Skerritt and Dr. Luca Motta observed that
the level of neurological pain a dog experiences can only be based upon
subjective evaluations of the dog's behaviors, which includes the dog's owner's
subjective observations.
In order to evaluate changes in the level of a dog's discomfort as
objectively as possible, to determine whether their surgical procedure on the
dog was successful (see
"syringosubarachnoid
shunt"
below) these neurosurgeons devised a Pain Score Scheme (see table
below) for the dog's owners to measure pain which the dog experiences from CM and SM,
particularly following surgery. Their pain score
scheme was created on the basis of different neurological grade classifications
previously suggested by other researchers, including the Cerda-Gonzalez / Olby 2009 study above. Mr. Skerritt and Dr. Motta evaluated their patients' histories and found some
specific information that could be used to create an objective pain score (i.e.,
frequency of scratching episodes and site of scratching, screaming episodes).
However, because of the inherent subjectivity of relying upon reports from the
dog's owners, they concluded that the design of a more robust scoring system
together with prospective studies was
warranted
In a
2012 study
UK researchers of cavaliers with neuropathic pain report on the results of far more
extensive questionnaires (using a 5-point scale), completed by the
owners of 122 CM/SM-affected CKCSs. They found that owners who noticed
evidence of neuropathic pain in their dogs also found the dogs to have
increased fear-related behaviors (such as acting more fearfully when
approached by strangers, or when in unfamiliar situations, or when
sudden loud noises occurred, such as thunderstorms). These dogs also were
more clingy to their owners and appeared to be more fearful when left
alone. They also showed decreased willingness to exercise, and problems
in settling, including sleep disturbances. Not surprisingly, the study
also showed that owners found that their affected dogs had reduced
quality of life.
In an effort to pinpoint the locus of the pain caused
by SM,  in an
August
2012 study
, researchers
compared the expression of two pain-related neuropeptides
in the spinal cord dorsal horn of normal dogs with the peptides'
expression in cavaliers with and without clinical signs of
syringomyelia. They discovered that there was a decrease in expression
of both peptides in CKCSs with symptomatic syringomyelia.
Peptides
are molecules formed by joining from two to about fifty amino acids. The
two neuropeptides in this study were substance P and calcitonin.
In
an
April 2013
study
of 26 cavaliers (11 dogs without clinical signs of pain; 6 dogs
with pain and symmetrical syrinxes; 9 dogs with pain and asymmetrical
syrinxes), German researchers
found "an association" between pain and SM
asymmetry, and they found "a strong association" between pain and dorsal
horn involvement of SM. CKCSs with clinical signs of pain showed either
In
May 2016 article
, UK researchers tested the electronic von Frey
aesthesiometer (eVF)
(at right)
on twelve cavaliers to determine if
they could quantify the dogs' cervical skin sensitivity. They decided that the
number of dogs was insufficient to reach any conclusions, and they announced
plans to study a larger group of CKCSs and divide them by CM/SM status. Their
aim is to establish a protocol to quantify neck pain in cavaliers with
neuropathic pain.
In a
November 2016 abstract
, UK researchers (H. Williams, S. Sanchis, H.
A. Volk, L. Pelligand, J. Murrell, N. Granger) tested 70 cavalier King
Charles spaniels for skin sensitivity using the eVF. The dogs were
categorized in three classes: (i) 37 dogs had syringomyelia and clinical
signs (syringomyelia-symptomatic - SM-S); (ii) 15 dogs had syringomyelia
without clinical signs (syringomyelia-asymptomatic - SM-A); and (iii) 18
dogs had no syringomyelia (syringomyelia-free - SM-F). The researchers
found that eVF assessment of skin sensitivity does not differ
significantly by syringomyelia status.
In a
July 2019 article
, a team of UK neurology researchers studied the
records of 130 cavalier King Charles spaniels diagnosed with Chiari-like
malformation (CM) and some also with syringomyelia (SM) to determine
which symptoms (clinical and behavioral signs) related to CM and to SM
and to syrinx diameter, in order to use the data in future studies of
diagnosis, treatment, and genetics of CM/SM. Dogs were grouped based
upon whether they had no SM (Group 1) up to having a syrinx greater than
4 mm (Group 4).
Signs found TO BE RELATED to syrinx
presence or size:
•  Phantom scratching -- 67% of Group 4 dogs and
none in other groups
•  Scratching or rubbing of the head or ears -- 28%
but less common in Group 4 dogs
•  Scoliosis -- 27% of Group 4 dogs and
none in other groups
•  Postural defects -- 15% of Group 4 dogs and none
in other groups
•  Weakness -- 39% of Group 4 dogs and none in other
groups
The researchers stated that their findings suggest that "phantom
scratching is highly unlikely with small syrinxes." They also found that
among the dogs in their study,
PSOM (primary secretory otitis media)
is
common in symptomatic CM-affected dogs and in SM-affected dogs, thereby
raising the possibility of confusing the cause of some signs and
behaviors, since PSOM-affected dogs tend to engage in ear-rubbing. They
concluded:
"The study further suggests that SM-specific signs are phantom
scratching, scoliosis, and sensory and motor signs that can be related
to spinal cord damage by the syrinx and are associated with large
syringes (transverse width >4 mm). Non-SM-specific signs include
vocalization (described as without obvious trigger, when shifting
position when recumbent and when being lifted under the sternum to a
height), spinal pain, head and ear rubbing or scratching, aversion to
touch, refusal or difficulty jumping or doing stairs, exercise
intolerance/reduced activity, sleep disruption, or behavioral change
described as becoming more anxious, timid, aggressive, or withdrawn.
These non-SM-specific signs could reflect CM-P [CM associated pain]."
The implication from this study is, therefore, that the major signs
of pain expressed by CM/SM cavaliers definitely are not due to having a
syrinx and probably are due to having Chiari-like malformation, but the
authors cannot definitely attribute the painful expressions solely to
CM.
In a
January 2025 YouTube video
, Dr. Clare Rusbridge observed that as
CM-affected cavaliers grow older, their brains shrink, and as a
consequence, the severity of fhe CM -- and thus the resulting pain --
may reduce.
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Changes in barometric
pressure
Some owners of CM/SM-affected dogs have reported anecdotally that
changes in barometric pressure due to weather conditions appear to
affect the levels of pain in their dogs. Scientifically-structured
studies on this topic have been limited to owners' answers to
researchers' questionnaires using grading  scores, such as a scale
of 1 to 10, and therefore are not very objectively reliable. Only two
such reports, discussed here below, have  been found, and in both
of them, the conclusion is that no evidence supports the hypothesis that
barometric changes affect pain level variations.
In an
April 2015
report
, UK researchers
compared daily barometric pressure changes with the comfort levels
(reported by dogs' owners in answers to questlonnaires) of 22 cavaliers
affected by CM/SM for 3 months.
They found no evidence supporting an association between barometric
pressure and the degree of pain symptoms displayed by CKCS with CM/SM.
They concluded:
"Currently, there is no evidence supporting an association between
barometric pressure and the degree of discomfort experienced by CKCS
with CM/SM. This appears contrary to the experience of some individuals
affected by these conditions. A more objective assessment of a larger
population of dogs is required to determine whether or not barometric
pressure has an influence on the comfort of some or all CKCS with
CM/SM."
In a
May 2015 master's thesis
a Netherland's researcher
reviewed the answers to questionaires by the owners of 848 cavaliers, 45
of which (19.3%) had clinical signs of CM/SM. The questions included
changes in pain symptoms related to different weather conditions,
including cold/ hot temperatures and high/low barometric pressures. The
researcher stated at the outset that some dogs appear to  show more
extreme symptoms during cold weather or low barometric pressure.
However, the
author reported:
"In this research there was no significant relationship between the
different weather influences and the sensitivity of the CKCSs. This
could be because owners are not really aware of the barometric pressure
and they do not link the grade of the symptoms with the barometric
pressure.  ... To really evaluate the effects of barometric
pressure and temperature on neuropathic pain in CKCS it would be more
reliable to do research in a climate controlled room and stimulate the
dogs in different ways to observe if they react more painful during the
different weather conditions."
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Other disorders with similar symptoms
Several of these signs are so common that they may be for other
reasons and unrelated to CM or SM at all. For example, prior studies
have shown that approximately 25%  of dogs that display clinical
signs of SM are not found to have a syrinx on MRI scans. See, e.g., this
December 2011
article
Another disorder common to cavaliers and with symptoms similar to SM is
Primary Secretory Otitis Media (PSOM)
, which is a highly viscous mucus
plug which fills the middle ear and causes the tympanic membrane to bulge.
Because the pain and other sensations in the head and neck areas, resulting
from PSOM, are so similar to symptoms due to SM, the possibility that the
cavalier has PSOM and not SM should be determined before diagnosing SM.
In a
brief July 2009 article
, UK researchers Dr. Richard J Piercy and
Gemma Walmsley disclosed that they had identified a genetic form of
muscular dystrophy
in the cavalier, with symptoms (weakness and exercise
intolerance) similar to some of those of SM.  However, these other
symptoms of this muscular dystrophy may clearly distinguish it from SM:
muscle atrophy, difficulty swallowing, and an enlarged tongue.  Also,
the researchers have found that only males are affected by this form of
muscular dystrophy, and the females are
only carriers of the mutation.
Dr. Curtis
Dewey has reported that in the course of his examination of
MRIs of cavaliers with Chiari-like malformation, he also has discovered
cerebellar infarcts (strokes).  He has written that CKCSs appear to be
pre-disposed to infarcts due to the presence of CM and that the existence of
both CM and infarcts "is common in the CKCS."  See
Cerebellar Infarcts
for details.
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Symptoms not due to CM/SM
Scratching the belly or chewing the paws are not signs of CM or SM.
If a dog engages in phantom scratching but does not have a wide syrinx
extending to the superficial dorsal horn (SDH) in the C3-C6 spinal
segments, then that dog most likely is not displaying a symptom of SM.
Seizures are not caused by CM or SM. Progressive paralysis of the
hind legs is not caused by CM or SM. CM/SM-affected dogs may display
some weakness in their hind legs, and they may stumble when they walk,
but they keep on walking nonetheless. So, paralysis of the hind legs
indicates, more likely,
intervertebral disc disease
or
degenerative myelopathy
Behaviors and physical signs customarily attributed to
epilepsy
fly
catching
facial
nerve paralysis
vestibular (balance)
disease
intervertebral disc disease
, and
degenerative myelopathy
(severe
and progressive hind limb weakness) are either not caused by CM or SM or
are highly unlikely to be associated with either CM or SM. These
disorders do not result in structural changes on MRI scans.
RETURN TO TOP
Diagnosis
Chiari Check Questionnaire
CHASE Questionnaire
Magnetic resonance imaging (MRI)
Computed tomography (CT)
Thermography (Medical infrared
thermal imaging)
Ultrasound
Brainstem auditory evoked response (BAER)
Physical examination
Machine learning
Severity of symptoms
Biomarkers
Gabapentin trial
Chiari Check Questionnaire
Chiari Check
is
a free, on-line questionnaire-based diagnostic tool which estimates the
likelihood of Chiari-associated pain (CM-P) and syringomyelia-associated phantom
scratching, based upon owner-reported answers to the questionnaire. This
tool is intended to support early decision-making, in advance of magnetic
resonance imaging (MRI), and improve access to diagnosis for CM/SM-affected
dogs, worldwide. Accurate dagnosis requires
magnetic resonance imaging
(MRI)
scanning, but limited access and high costs often delay
treatment.  Watch this explanatory video on
YouTube at this link
In this
September 2025 poster
presented at the 2025 European College of
Veterinary Neurology (ECVN) Symposium, the results of submissions of
1,091 dogs of 62 breeds and cross-breeds, 80% of which were cavalier
King Charles spaniels, are described.
RETURN TO TOP
CHASE Questionnaire
In a
January 2026
article
, researchers at North Carolina State University and Ohio
State University devised a questionnaire for owners of dogs diagnosed with
Chiari-like malformation and syringomyelia (CM/SM) to assess their dogs'
responses to pain treatment with pregabalin and placebo during periods
of 2 weeks each. There were 2 groups of dogs, a healthy group of 20,
including 2 cavalier King Charles spaniels, and a CM/SM-affected group
of 30 cavaliers. Each week of treatment, the owners completed the CHASE
(Chiari-like malformation and syringomyelia evaluation) questionnaire to
assess their dogs' response to treatment. The CHASE questionnaire
consists of 5 categories -- Scratching (displaying visible signs of
irritation), Anxious (displaying nervousness or worry), Sensitive
(easily upset or hurt), Uncomfortable, and Restless -- and the main
question is "Please think about how your dog has behaved over the past
week and use the scale to tell us how well the phrases describe your dog
or what he/she is doing." They concluded:
"Our results support that the CHASE questionnaire is capable of
successfully capturing behaviors that are believed to be a consequence
of neuropathic pain and itch in dogs with CM/SM. This conclusion is
strongly supported by the responsiveness of the component questions and
overall score to the clinical signs of the condition. The final CHASE
questionnaire was simple to administer remotely, owners answered the
questions consistently, and it discriminated between healthy and
affected dogs. In addition, it detected appropriate changes in clinical
signs in canine CM/SM patients receiving a treatment of known efficacy
in a double-blinded, randomized controlled trial. Robust repeatability
also was observed, evidenced by the lack of significant difference in
CHASE scores at both timepoints in the healthy cohort and between
screening and baseline CHASE scores in the CM/SM cohort."
RETURN TO TOP
Magnetic resonance imaging (MRI)
Dynamic
susceptibility contrast perfusion MRI
Diffusion tensor
imaging (DTI)
The
most accurate way of diagnosing the Chiari-like malformation and
syringomyelia is
said to be through the use of
magnetic resonance imaging (MRI) scanning.
The MRI allows the veterinary neurologist or neurosurgeon to study the
skull and spine for the presence of  any abnormality which might
obstruct the flow of the cerebrospinal fluid.  When examined by MRI,
the syringomyelia appears as a tubular cavity of fluid, called a syrinx,
within the spinal cord. In severe cases, the syrinx is so wide that only a
thin rim of the spinal cord is visible.  An MRI scan of a dog without
any syrinxes at all still may show that the dog has Chiari-like
malformation.
Clinic charges for MRI
examinations of canines have been known to vary from $400.00 to over
$2,000.00.
Accurate MRI results require that usually the dog be
anesthetized.  In view of the high cost of MRI scans, the examing
veterinary specialist usually will attempt to rule out other causes of the
symptoms first. Veterinarians who perform MRIs of should consider following
this
MRI Screening Protocol
devised by Dr. Rusbridge.
See our list
of low-cost MRI clinics
here
While MRI is considered "the gold standard" in diagnosing both CM and
SM, as well as the degree of each, MRI is not without error. MRI is
limited to providing images of the structure of the brain and spinal
column. It requires
the examiner to make certain viewing decisions, such as the angle for
transverse images, and if that angle is not perpendicular to the dog's
spinal cord, the images may artificially enlarge the central canal and
result in an incorrect diagnosis. Also, the abilities and experience
levels of the examiners have been shown in studies to play an important
role in the accuracy of their analyses. Radiology diplomates with
decades of experience are much better equipped to accureately diagnose
the disorders and grade their degrees than are less experienced
examiners. See this
April 2020 article
for a discussion of the comparisons in abilities
of MRI examiners regarding cavaliers with or without CM and SM.
MRI scans cannot confirm that pain is due to either CM or SM. If a dog
diagnosed with CM/SM displays indications of pain, the neurologist must
eliminate other possible causes of that pain.
The MRI scan of a cavalier below at the right shows the occipital malformation,
with the cerebellum being squeezed out of the occipital bone and into the
area of the foramen magnum (red-outlined area).  It also shows pockets
of white cerebrospinal fluid in the spinal cord (yellow-outlined area).
See Karen Kennedy's
Basic Canine NeuroAnatomy and MRI Imaging Planes,
for further
information about MRI scans.
In a
2011 study
conducted by Drs. Rusbridge and Knowler,
in a sample of seventy "unaffected" cavaliers from Europe and North America, which were
MRI-scanned only for breeding purposes, 70% of them had syringomyelia, 17%
were "at risk", meaning were young dogs with Chiari-like malformation but no
syringomyelia yet, and only 13% were "clear" of both the malformation and
SM.  In February 2010, Dr. Georgina Child
board certified veterinary neurologist in
Australia, reported that of 60 asymptomatic cavaliers scanned as potential
breeding stock, 50% had SM syrinxes.
In
MRI studies of 49 cavaliers
reported in 2011 in the Veterinary Journal, Dr. Rusbridge and others found
that "Syrinx formation was present in the C1-C4 region and in other parts of
the spinal cord. The maximal dorsoventral syrinx size can occur in any
region of the spinal cord." Seventy-six per cent of CKCS with a a cranial
cervical syrinx also had a syrinx in more caudal spinal cord regions.
Therefore, so-called "mini-MRI-scans" of only the cervical region, such as
those scans for
breeding protocol purposes
, may
not necessarily locate all syrinx which an SM-affected cavalier may have.
Dr. Curtis
Dewey
has reported that in the course of his examination of
MRIs of cavaliers with Chiari-like malformation, he also has discovered
cerebellar infarcts (strokes).  He has written that CKCSs appear to be
pre-disposed to infarcts due to the presence of CM and that the existence of
both CM and infarcts "is common in the CKCS."  See
Cerebellar Infarcts
for details.
Also, benign, small syrinxes are a common incidental finding on MRI
examinations. Therefore, clinical
correlation is important in order
to determine if the syrinx is associated with the Chiari-like
malformation and/or symptoms.
The following MRI photographs, and their descriptive text, are courtesy
of
Dr. Clare Rusbridge
and
Dr. Penny Knowler of Stone Lion Veterinary
Centre:
For more MRI views of cavaliers with syringomyelia or the Chiari-like malformation,
see Karen Kennedy's
Understanding Canine Chiari Malformation and Syrningomyelia
and
Related Links
below.
Karen Kennedy,
RTMR, MappSc, is a magnetic resonance imaging specialist with The London
Health Sciences Centre, London, Ontario, Canada.
Karen Kennedy,
RTMR, MappSc, is a magnetic resonance imaging specialist with The London
Health Sciences Centre, London, Ontario, Canada.
In a
November 2018 article
, Drs. Clare Rusbridge and Susan P. Knowler and
Felicity Stringer have thoroughly summarized the current research
knowledge about symptomatic Chiari-like malformation (CM) and
syringomyelia (SM) in cavalier King Charles spaniels and other affected
breeds. Their work includes handy charts covering the topics of skull
changes, craniocervical junction and cervical changes, neuroparenchymal
changes, syrinx features, MRI protocols, and interpretations of MRI
scans for diagnosing CM pain and symptomatic SM. They also have
comparison MRI scan views of cavaliers with varying stages of CM and SM,
including Figure 8, below, comparing the MRI scans of three CKCSs.
Dynamic
susceptibility contrast perfusion MRI
Dynamic susceptibility contrast perfusion magnetic resonance imaging
(DSC-PMRI) enables the quantification of the volume of blood passing
through the brain tissue.
In
an
August 2017 article
, researchers  studied the ventricle system
of 42 cavalier King Charles spaniels -- 32 CKSCs with
ventriculomegaly
and 10
control CKCSs -- using DSC-PMRI.
Diffusion tensor imaging
(DTI)
Diffusion Tensor Imaging (DTI) is an advanced form of magnetic
resonance imaging (MRI) that uses multiple MRI scans, performed in
numerous different directions, of the same limited regional tissues of
the brain or spinal cord (called voxels) to create a 3-dimensional image
showing the directions in which  water molecules diffuse in the
tissue.
In a
December 2022 article
, a team of Polish veterinary researchers examined 30 cavalier King Charles
spaniels, 18 of which were confirmed by MRI to have syringomyelia (SM)
and 12 CKCSs without SM. Of the 18 CM/SM-affected dogs, 8 were
symptomatic and 10 were not. All dogs underwent diffusion tensor imaging
(DTI), a MRI modality which can provide a detailed assessment of the
intrinsic spinal tracts and a better understanding of how tissue damage
causes clinical deficiencies. It is a non-invasive MRI technique which
is more sensitive to microstructural changes than conventional MR images
and is able to show abnormalities within the spinal cord which are not
visible on standard structural MR images. It measures microstructural
characteristics of water diffusion within the nervous tissues. They
report finding a difference in two DTI parameters: (1) fractional
anisotropy (FA) and (2) apparent diffusion coefficient (ADC) between
nonsymptomatic and symptomatic cavaliers. They concluded that the use of
DTI imaging in the MRI evaluation of CM/SM dogs (and humans) may be
useful in devising a protocol for an objective assessment of the spinal
cord and to understand what processes lie at the basis of many diseases,
the diagnosis of which is currently difficult.
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Computed tomography (CT)
Dr. Dominic J. Marino of Long Island Veterinary
Specialists (LIVS) reported in October 2007 that evaluation of the entire
skull shape and size utilizing Spiral CT technology with 3D reconstruction
is currently underway to identify additional mechanisms of syrinx formation.
He wrote that CT scanning may enable surgeons to focus on correcting the
flow of CSF as the malformation affects its normal passage around the brain
and spinal cord and leads to the syrinx formation known as syringomyelia.
In a
2013 study
of nine cavaliers with neurological disorders, a team of Ghent
University (Belgium) veterinary radiologists compared the dogs' MRIs and CTs and
concluded:
"The statistical analysis suggested that both techniques are
useful for detecting CH [cerebellar herniation]. However because the bias was
significantly different from zero, one of the methods consistently led to the
determination of longer or shorter HL [cerebellar herniation length] than the
other method. For most comparisons, the HL was on average longer on CT. MRI
provides greater soft tissue detail with no beam-hardening artifacts, which may
improve the delineation of the cerebellum. Because HL does affect a diagnosis of
CM, so CT can be used as a primary diagnostic tool for diagnosing CM in CKSs
when MRI is not available."
In
a November 2014 study
of 15 cavalier King Charles spaniels
by a team of Belgian researchers, they compared computed tomography (CT)
scans with MRI scans and analyzing them statistically, they found "no
significant difference between the different observers and techniques
for the detection of CH [cerebellar herniation] and measurement of CHL
[cerebellar herniation length]." However, they found, "Overall, the CHL
was longer on the CT images." They concluded:
"Both techniques are useful for detecting CH and measuring CHL.
Because CHL does not have a known direct impact on the clinical
presentation of CM, CT can be used as a diagnostic tool in a routine
clinical practice for CM in CKCS when MRI is not available. We emphasize
that MRI is the standard screening technique in CKCS for breeding
purposes to detect the presence of CM and SM and, at the current time,
CT cannot replace MRI."
In
an
August 2015 report
, a team of Belgium researchers compared computed
tomography (CT) and magnetic resonance (MR) scans of 32 dogs, including
12 cavalier King Charles spaniels. They found that low-field MR and
multislice CT imaging provided comparable information regarding the
presence of SM, and that CT can be used as a diagnostic tool for SM when
MRI is not available. They conclude, however, that "CT cannot replace
MRI as the standard screening technique for the detection of SM in
Cavalier King Charles Spaniel for breeding purposes."
In an
April 2020 article
, Ohio State
researchers compared
MRI with CT for grading CM and SM in 30 cavaliers The study
also included three classes of observers with different levels of
experience -- two American college of veterinary radiology diplomates
(DACVR) and two second-year veterinary radiology residents and two small
animal veterinary interns. They point out the reason for the study is
that, "Computed tomography is financially cheaper, shorter in
acquisition time, more accessible to general practitioners, and requires
less anesthetic drugs/time."
(See Figure 2, above.)
The results of the study support the
hypothesis that the overall agreement and the agreement between observer
groups of similar experience levels is higher using MRI compared to CT.
As expected, the accuracy for diagnosis by experienced radiologists of
cerebellar herniation and SM using MRI was higher than CT. However, CT
had a higher accuracy among the second-year radiology residents and
veterinary interns for identifying cerebellar herniation, which
countered the investigators' hypothesis that MRI is a better tool for CM
evaluation. They concluded:
"Computed tomography does not replace MRI for the diagnosis and
classification of CM and SM in CKCS. The accuracy and agreement for
identifying cerebellar herniation and SM in experienced observers was
higher utilizing high-field MRI compared to multislice CT. Breeding
programs for CKCS should continue to utilize MRI for antemortem diagnosis
of CM and SM to help improve the genetic pool and minimize the risks for
neuropathic pain brought about by CM and SM. Individuals with greater
diagnostic imaging experience (DACVR) resulted in better agreement for
both MRI and CT and higher sensitivity, specificity, and accuracy for
cerebellar herniation and SM. Magnetic resonance imaging interpreted by
experienced observers should remain the standard tool for CM and SM
screening programs."
Additionally, CT  reportedly cannot replace MRI for breeders'
screening purposes, because CT cannot detect presyrinx and cannot detect
fluid in the syrinx.
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Thermography (medical infrared
thermal imaging)
Medical infrared thermal imaging (MITI) is also
known as medical infrared imaging (MII) and as infrared
thermography (IRT).
In a
June 2011 study
of 105 cavalier
King Charles spaniels, Drs. Marino and Catherine Loughin found
that MII was up to 97.3% accurate in identifying dogs with CLM. They concluded,
"Based on these preliminary findings, MII may be a viable screening tool to
detect CLM in dogs." In a
March 2020 article
, the same team of US neurological researchers studied medical infrared
thermal images (MITI) of 93 cavalier King Charles spaniels to determine if MITI
could detect syrinxes in cavaliers diagnosed by MRI as having syringomyelia
(SM). All 93 dogs had been examined by MRI and found to have Chiari-like
malformation. Of those, 48 were diagnosed with SM and 45 had no evidence of SM.
The authors tested MITI devices using a variety of texture distances, finding
that a distance of 6 produced the best results -- 69.9% accuracy in detecting
syrinxes known by MRI to be present. They concluded:
"This study revealed that MITI is a successful screening test for the
presence of SM in CKCS with CLM. Compared to other imaging modalities,
MITI is a quick, inexpensive modality that does not require sedation nor
anesthesia, and eliminates radiation exposure (to patient & staff). MITI
does not provide insight to syrinx location or severity nor should it be
used as a sole diagnostic modality. While veterinary thermographic
imaging continues to improve as advances in technology occur, MRI will
remain the gold standard for definitive diagnosis and staging of
Chiari-like malformation and syringomyelia."
Figure 1: Thermograms of CKCS: Left image is CKCS without SM; right image
is CKCS with SM
Beginning in October 2012, a UK clinic, Veterinary Thermal Imaging Limited,
has been studying thermal imaging to detect of dogs to detect Chiari-like
malformation and syringomyelia. The procedure used to explore the use of thermal
imaging for the screening of CLM is non-invasive. Thermal images are taken of
the dog's head and neck. The images can be taken without the need for sedation,
and in the dog's home. The thermographer then examines these images, along with
MRI results, to see if a correlation can be seen between skull and neck
structures in the affected animals. Veterinary Thermal Imaging Limited is
located on Hale House Lane, Churt, Surrey, GU10 2JG. For more information,
contact Stephanie Godfrey at Stephanie.godfrey@vtiuk.com,
telephone 0844 544 3314, website
www.veterinary-thermal-imaging.com
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Ultrasound
In the same
2008 French study
reported under computed tomography above, one dog's
syrinx was identified by ultrasound.  The researchers found that
ultrasonography probably has too low a sensitivity for reliable diagnosis of
Chiari-like malformation/syringomyelia.
In an
August 2008 report
by
German researchers using ultrasound as a comparative imaging technique to
MRIs, they compared 10 normal brachycephalic dogs with 25 cavaliers known to
have Chiari-like malformation. They found that "Cerebellar displacement into
the foramen magnum was clearly identified sonographically; however,
syringohydromyelia was not discernable due to bone overlay."
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Brainstem auditory evoked response (BAER)
As of October 2007, Dr. Marino reported that "38 Cavalier King Charles
Spaniels had been evaluated thus far. One dog had a normal MRI, BAER, and
thermographic evaluation. Twenty-three dogs without clinical signs had
abnormal MRI findings with 16 of the 23 dogs (69.6%) also having
abnormalities with BAER testing. Fourteen dogs with clinical signs had
abnormal MRI findings and 13 of the 14 dogs (92.8%) also had abnormal BAER
tests. BAER testing may play a more useful role in screening 'clinical' dogs
rather than dogs without clinical signs.
In a
2010 report
, a
group of Canadian neurologists tested fifty cavaliers to evaluate the
validity of BAER as well as transcranial magnetic motor evoked potentials
(TMMEP), somatosensory evoked potentials (SSEP), and spinal evoked
potentials (SEP), compared to MRIs.  The researchers found: "TMMEP,
SSEP, SEP and BAER do not appear to be valuable tests in detecting
functional abnormalities of the motor and sensory pathways throughout the
central nervous system of CKCS dogs with and without neurological signs
secondary to SM diagnosed by MRI."
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Physical examination
In a
2014 study
of 133 cavaliers, researchers examined their skulls to determine if skull measurements could predict the presence or
development of syringomyelia (SM), They found that as the dog's cranium
is shortened and broadened, the risk of developing SM increases. They stated:
"The study found two aspects of conformation to be
associated with the development of SM in the CKCS: the cephalic index
and the distribution of cranium across the length of the head. It was
found that a higher cephalic index and, separately, a lower percentage
of the cranium distributed caudally were significantly associated with
disease development."
"The cephalic index is the ratio of the
width of the cranium of an organism (taken behind the cheekbones in this
study) divided by its length (i.e., in the horizontal plane, or front to
back). It is usually expressed as a %. It differs from craniofacial
index in that it does not relate to the length of the muzzle."
"The conformational indicator of caudal cranium distribution was found
to significantly, correctly classify cases as SM clear or affected at
the level of three years of age, five years of age, and when comparing a
sample of SM clear dogs over five years to those affected and younger
than three. Cephalic index was able to significantly, correctly classify
cases at the latter level. Results suggest that these indicators are
irrelevant of age (after 18 months of age), gender and parity. These,
therefore, represent invaluable tools in determining breeding plans in
that they are not only protective against developing the condition in
the first three years of life but they are protective against developing
the condition at all, maintaining SM clear status beyond the age of five
years."
This
confirmation indicator research is not a diagnosis, but is to aid in
risk assessment to provide breeders with a tool to use with their
breeding stock. See
also this
YouTube video explaining this article
In a
June 2018 abstract
presented to the 2018 ACVIM Forum, UK researchers
relied upon an innovative machine learning technique (a computerized
data analytics technique using computational methods to learn
information from data without relying on a predetermined equation as a
model). The team obtained MRI scans of 66 cavalier King Charles spaniels
(CKCSs) over the age of 4 years. Of them, 26 did not have syringomyelia
(SM) and 40 had SM with a syrinx width of at least 4 mm. They performed
morphometric analysis of the shape and position of the soft palate in
relation to the skull base and the rostral (towards the oral or nasal
region) flattening of the forebrain. In the SM dogs, the distance
between the rostral (again, towards the oral or nasal region) end of the
soft palate and (a) the sella turcica (a saddle-shaped depression in the
body of the sphenoid bone of the human skull, where the pituitary gland
sits), and (b) the foramen magnum basioccipital portion of occipital
bone, was significantly shorter than the non-SM control group of dogs.
The shorter distance between the brain and the frontal bone also was
highly significant in SM-affected dogs. They concluded that CKCSs with
SM have a flattening of the frontal portion of their skulls, when
compared to non-SM cavaliers.
In a
January 2019 article
by a team of UK and Swedish researchers, 13
cavalier King Charles spaniels were examined by UK breed judges, using
a checklist
, to determine if the risk of Chiari-like malformation
(CM) and syringomyelia (SM) could be identified by visual assessment of
head shape. The results showed a positive correlation between the
judges' evaluations and the risk of CM/SM sufficient to warrant a larger
study of the breed. Figure 5 (
below
) shows the most extreme
range of checklist scores. The researchers concluded:
"This prospective investigation demonstrated that it was possible to
compare subjective evaluation of head conformation with objective
measurements and revealed a significant correlation between the
subjective visual evaluation of head conformation and an objective
evaluation of dorsoventral doming using photographs. However, this
pilot investigation demonstrated that individual adjudicators can
vary in their interpretation of the CKCS breed type and also
suggests that measuring the cephalic index or rostrocaudal doming
alone is not a reliable indicator of brachycephaly but should be
taken together with a visual evaluation and take account of other
features, such as those on the checklist and the size of the dog."
In a
November 2019 article,
a team of UK researchers reviewed the medical
records of 66 cavalier King Charles spaniels (CKCS), 40 of which had
syringomyelia (SM) and the other 26 did not; 55 had Chiari-like
malformation (CM) and 11 did not. The dogs were grouped by (1) control
group of 11 with no Chiari-like malformation (CM-N); (2) CM pain group
(CM-P) of 15 dogs; (3) clinical SM group (SM-S) of 40 dogs. SM-S dogs
included those with outward symptoms of SM (variable phantom scratching,
scoliosis, etc.) and a syrinx of at least 4 mm. The researchers divided
their study into two sub-sets, the first examined head features related
to the dogs' soft palates, and the other examined features related to
their hard palates; both sub-sets also included review of the dogs'
features related to forebrain flattening and olfactory bulb rotation.
The olfactory bulb is a bulb of neural tissue within the dog's
fore-brain. Their work included comparing the shape of the "stop" of
each dog, which is the degree of the angle where the nose and skull
meet, and the indentation between the eyes at that point. A "gentle
stop" has the least angular shape and a "pronounced stop" has the
sharpest angle.
They found
(see figure 5 below)
• CM-N dogs (no CM) had the least brachycephalic head, a gentle stop
with the greatest upper jaw area between the hard palate and the
frontal bone, and the longest soft palate length.
• CM-P dogs
(painful CM) had the least distance between the hard palate and
cranium, a pronounced stop, and a displaced olfactory bulb.
CM-S dogs (large syrinx) had the most reduced middle craial bone
area and shortest distance between the connection of the hard and
soft palates with the base of the cranium.
They conclude that dogs with CM-P had the shortest muzzle lengths,
and that "a reduced distance between the hard palate and the frontal
bone was particularly associated with CM-P." Dr. Clare Rusbridge, one of
the researchers, explained:
"Dogs with clinically relevant CM/SM are more likely to have
brachycephalic features of the rostral skull flattening with
reduction of nasal tissue and a well-defined stop. This evidence not
only enhances our understanding of the disease and 'at risk' head
conformation but could also impact on the assessment of MRI and
disease diagnosis. It suggests the whole skull should be analyzed
and not just the hindbrain currently required in prebreeding
screening. This information has implications not only for breeders
and pet owners but also for the veterinary profession to raise
awareness about the welfare aspects of breeding. Furthermore, an
increased risk for SM and painful CM might not be confined to
brachycephalic breeds but other miniaturized purebreeds and hybrids
that have gained in popularity as pets."
Co-researcher Dr. Susan P. Knowler explained:
"This study suggests that the whole skull, rather than just the
hindbrain, should be analysed in diagnostic tests. It also impacts
on how we should interpret MRI from affected dogs and the choices we
make when we breed predisposed dogs and develop breeding
recommendations. ...
The
brachycephalic features that can be seen from outside is a head that
has flattening at the front with reduction of nasal tissue and a
well-defined stop."
Ga
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Machine learning
"Machine learning" (ML) is an artificial intelligence device using
statistical algorithms and models to analyze and draw inferences from
patterns of information.
Chiari Check
is
a free, web-based diagnostic tool developed to aid in
assessing the likelihood of pain
caused by Canine Chiari malformation
and syringomyelia in dogs. Chiari Check uses a Machine Learning model,
enabling veterinarians and caregivers to upload clinical signs via a
detailed questionnaire. The tool uses algorithms to predict the
likelihood of disease.
UK researchers Kristiana Ivanova, Clare Rusbridge, and Mariam Cirovic
introduced Canine Check at the March 2024 BSAVA 2024 conference, They presented a poster
(at
right -- click to enlarge it)
announcing the creation of a machine
learning tool available online that can predict the likelihood of
painful Chiari-like malformation (CM-P) in cavaliers and other breeds.
In this project, data from 185 dogs diagnosed
with CM-P and syringomyelia (SM) together with the dogs' owners answers
to a series of questions about their dogs' symptoms and behaviors. The
model program called Naive Bayes model ("MICE NB all combined")
performed best against the evaluation metrics and test data, for both
predicting CM-P and SM.
The researchers concluded that their tool
supports suspected diagnosis when further diagnostics, such as MRI
scans, are restricted due to their costs. They stated that:
"The collected data provides researchers better insight into common
clinical indicators of CM-P and SM for diagnosis, monitoring
effectivenes of treatment, and assessing quality of life."
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Severity of symptoms
In the absence of an MRI, the severity of certain SM-related symptoms
and their combinations have been found to indicate the size range of
syrinxes in cavaliers. In a
February 2024 article
, Danish researchers investigated
the symptoms of 89 cavaliers which had been
diagnosed with SM by MRI at the University of
Copenhagen, Denmark. They interviewed the dogs' owners, to determine the
relationship between the sizes of the dogs' syrinxes and their
SM-related symptoms. The severity of the dogs' CM and SM were cagtegorized by the
British Veterinary
Association/Kennel Club scheme
of measuring the condition of the CM and
sizes of the syrinxes. The dogs were distributed into three groups: (1)
dogs with CM and no SM (or with a maximum transverse width < 2 mm), (2)
dogs with CM and small syrinx (SM 2.00-3.99 mm) and (3) dogs with CM and
large syrinx (SM >4 mm). They report finding that these clinical signs
were reported significantly more frequently in dogs with large syrinxes:
• Phantom scratching
• Scratching of both sides of the neck and
shoulders
• Aversion to being touched to the head, neck, or shoulders
Worsening of clinical signe when the dog was emotionally aroused
Preferred head posture during sleep
They found that when phantom scratching, aversion to touch, and a
preferred head posture while asleep were combined, the likelihood of a
large syrinx increased. They concluded that clinicians may use this
information to diagnose CKCSs with a large syrinx and necessary
treatment when MRI diagnosis is not available or affordable.
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Biomarkers
Calcitonin gene related peptide (CGRP) is, obviously, a peptide. It is
produced primarily by cells in the thyroid and is secreted into the
nervous system, where it is stored.
In a
June 2024 report
to the ACVIM Forum 2024, In a study of29 cavaliers,
15 were diagnosed with CM/SM by MRI. Of those 15, 13 displayed symptosms
of pain and 12 were scratching. Lumbar CSF was collected from each dog,
and concentrations of CGRP from the CSF was correlated with the clinical
signs of pain and itching. The investigators found that CGRP
concentrations were elevated in cavaliers exhibiting pain and itching.
The investigators concluded that CGRP may contribute to neuropathic pain
in CM/SM-affected dogs, and that it could be a target for therapy.
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Gabapentin trial
If the dog is suspected to have CM/SM but its symptoms are mild, it
may not be necessary to have the dog diagnosed by MRI or any of the
electronic alternatives described above. A thorough physical examination
by a neurologist may be all that is needed to enable the veterinarian to
prescribe medications, typically
gabapentin
which may manage the suspected CM/SM. This commonly is called a
respnse-to-treatment approach, and more specifically a
"gabapentin trial". If the drug appears to resolve the symptoms, or at
least improve them, then SM may be assumed without having to conduct
further diagnosis. This may be the best course if the dog also has
mitral valve disease or is elderly and the owner does not want the dog
to have to endure the anesthesia necessary to conduct the MRI.
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Reduced Rate
MRI Clinics
in United States and Canada
The names and locations of veterinary neurologists who are board
certified by the American College of Veterinary Internal Medicine (ACVIM)
are on our
Neurologists
webpage.  Some MRI clinics which are offering reduced
rates for partial scans of cavaliers are listed below.
Be aware that
prices for MRI scans at these clinics are subject to change
and may not
include other services which are necessary for a complete analysis of the
dog's condition. Veterinarians who perform MRIs are advised to follow the
MRI Screening Protocol
The UK's cavalier club also offers
this list of MRI clinics
throughout the world.)
AUBURN, AL:
Auburn University's small animal teaching hospital is offering MRI scans for $1,010.00,
limited to cavaliers and Brussels griffons at least one year old and
asymptomatic (showing no signs of CM/SM). Appointments are available only on
Thursdays. Pre-anesthetic testing (blood work and thoracic radiographs) must
be performed by a veterinarian elsewhere within two weeks of the CM
screening appointment. The CM screening package includes:
Physical and neurologic examination by the neurology/neurosurgery service
• General anesthesia
• MRI of the head/neck
• Two CD
copies of the MRI images
• Breeding advice based on a previously
published grading scheme from the British Veterinary Association.
Bailey
Small Animal Teaching Hospital is located at 1220 Wire Rd., Auburn, AL
36849. Contact Dr. Amy B. Yanke (Email:
aby0003@auburn.edu
) at 334-844-4690
for more information. Website:
www.vetmed.auburn.edu
LOS
ANGELES, CA:
Dr. Veronique Sammut
board certified veterinary neurologist, offers mini-scans for
$1,220.00, which include mini MRI, IV catheter and IV fluids during
anesthesia, a copy of the MRI on CD and interpretation. The scan is from the
inter-thalamic adhesion to C5 or lower. It also covers axials of the
tympanic bullae to evaluate for PSOM ("glue ear"). A consultation is
required prior to scheduling procedure, not included in price above. Pre
anesthetic work up within 3 weeks of planned anesthesia is also required,
also not included in price above. Contact Lily Medrano at VCA-West Los
Angeles, at 1900 S. Sepulveda Blvd., Los Angeles, CA, 90025, Tel:
310-473-2951, Email:
lily.martinez@vca.com
website: https://vcahospitals.com/west-los-angeles/specialty
REDWOOD
CITY, CA:
AnimalScan at 410 Brewster Avenue, Redwood City, CA 94063,
telephone 650-480-2001, email
info@animalscan.org
website
animalscan.org
NAPLES,
FL
Dr. Michelle
Carnes
, board certified veterinary neurologist at Animal Specialty
Hospital of Florida, offers an MRI package for asymptomatic (non-clinical)
patients at $900.00 (for three or more dogs), $1,000.00 (for two dogs), and
$1,100.00 for one dog. The MRI scan is a mini-scan from interthalamic
adhesion to C5. The price includes a neurologic exam/physical prior to the
scan and a consultation following the scan for review of study, anesthesia,
a written interpretation of the scan, and a copy of the MRI on a CD.
Bloodwork is required and is not included in the price. Bloodwork should be
no older than two weeks. A report from a board certified veterinary
radiologist can be obtained for an additional fee.  For more information,
contact Eric Carnes, telephone 239-263-0480, email
ecarnes@ashfl.com
.  Animal Specialty Hospital of Florida is located at
10130 Market Street, Suite 1, Naples, Florida 34112, telephone:
239-263-0480, fax: 239-263-0488, website:
www.ashfl.com
FORT
WAYNE, IN
: Advanced Animal Imaging offers Cavalier breeders a
$495.00 mini-scan MRI per dog, which includes a consultation, reading of the
scan, and anesthesia. Pre-screening bloodwork is required prior to
anesthesia and is available for $75.00 at the Indian Creek Veterinary
Hospital in the same building. The clinic follows Dr. Rusbridge's
SM MRI screening protocol
Contact the clinic at telephone 260-434-1555 to make appointments. Advanced
Animal Imaging is located at 5902 Homestead Road, Fort Wayne, IN 46814, and
its website is
www.advancedanimalimaging.com
AMES,
IA:
The Lloyd Veterinary Medical Center at Iowa State University
offers a mini-scan MRI package at approximately $800.00, consisting of an
examination, MRI scan, and anesthesia. To schedule an appointment, call the
neurology service at 515-294-4900. It is located at 1600 S. 16th Street,
Ames IA 50011, and its website is
vetmed.iastate.edu/vmc
OVERLAND PARK, KS:
Dr. Brian C. Cellio
, board certified veterinary neurologist at
Veterinary Specialty and Emergency Center in Overland Park, Kansas (near
Kansas City) offers Cavalier breeders a $900.00 mini-scan MRI per dog for a
minimum of five dogs up to ten dogs per day.   Contact Dr.
Cellio's technician, Mandi, telephone  913-642-9563 or 800-413-6851 to
make appointments.  The clinic is located at 11950 West 110th Street,
Suite B, Overland Park, KS 66210, and its website is
www.vseckc.com
COMMERCE, MI:
Drs.
Michael Wolf
Jared B. Galle
and
Andrew Isaacs
board certified veterinary neurologists at Animal Neurology & MRI Center in
Commerce, Michigan, offer Cavalier breeders reduced rates as low as $975.00
for an MRI scan. Rate includes a neurological examination, anesthesia, MRI
scan and consultation/review of the MRI study with the neurologists, for a
minimum of three dogs. Review and MRI imaging report from their board
certified radiologist can be requested for an additional fee. Contact Dr. Wolf at the Animal
Neurology & MRI Center, 1120 Welch Road., Commerce, MI 48390, Tel:
248-960-7200, email
DrWolf@animalneurology.com
, website
www.animalneurology.com
STARKVILLE, MS:
Dr. Andy Shores
, board
certified veterinary neurologist at Mississippi State University (MSU),
announces that the Mississippi State College of Veterinary Medicine is
offering a breeding MRI screening program for CKCS and Brussels Griffon
breeders. Owners may bring or fax copies of blood and urine analyses from
their veterinarian or these tests can be performed on-site (for an
additional fee). A complete physical and neurologic examination will be
performed as part of the screening process along with a CT metal scan before
the MRI. Sedation/anesthesia, including an IV catheter and full and constant
monitoring will be provided. A MRI screening (3T magnet: Sagittal T2,
Transverse T1 and T2) will be performed. This also screens for primary
secretory otitis media (PSOM). The approximate total cost for 2 patients is
$1700; however, if MSU screens more than 2 patients, the cost will be
approximately $850.00 for each additional patient. The multiple patients
screening is designed to accommodate owners with several dogs being
considered as part of a breeding program. For the pricing break, MSU needs
to screen at least 2 patients at each setting. Contact Dr. Shores' office at
662-325-7339.
COLUMBIA,
MO:
University of Missouri's College of Veterinary Medicine (Drs.
Joan R. Coats
Dennis P. O'Brien
, and
Fred A. Wininger
offers CM/SM scans for $600.00, which includes "iso" anaesthesia.
Blood work is additional and may be obtained ahead of time at your
veterinarian's office. Contact Stephanie Gilliam, Neurology/Neurosurgery
Technician, University of Missouri Veterinary Medical Teaching Hospital, 900
E. Campus Drive, Columbia, MO 65211, telephone 573-882-7821.
RALEIGH, NC:
AnimalScan, at North
Carolina State University's College of Veterinary Medicine's Department of
Clinical Sciences, 4700 Hillsborough Street, Building 3, Raleigh, NC 27606,
telephone 919-838-5209, email
raleigh@animalscan.org
website animalscan.org
AKRON, OH:
Pets Dx
Veterinary Imaging, Inc. in Akron, Ohio and Pittsburgh,
Pennsylvania, offers a partial MRI, at reduced group
rates for Cavaliers, focusing on the head and neck, and includes a compact
disc with an imaging program.  Their MRIs may be reviewed, for an
additional fee, by Dr. Patrick R. Gavin, Diplomate ACVR, Professor of
Radiology, Washington State University College of Veterinary Medicine, in
consultation with the dog's veterinarian.  Pets Dx Veterinary Imaging,
Inc. is located at 1321 Centerview Circle, Akron, Ohio 44321, telephone
330-576-6275, and at 807 Camp Horne Road, Pittsburgh, PA 15237,
telephone 412-486-4800 and 412-348-2577. Its website is
www.petsdx.com
LONDON,
ON:
Thames Valley Veterinary Services in London, Ontario offers
reduced cost MRIs for Cavalier breeders, through the efforts of the
CKCS
Club of Canada
.  Current prices (as of June 2014): $475.00 CDN for
a mini scan (not including blood work); $575.00 CDN for a full scan (not
including blood work).
Participants will also receive an MRI that meets all
current scanning protocols, a CD copy of their MRI screening, and a report issued by
a specialist. Contact Mary Beth Squirrell of the CKCS Canada club for more
information, email
mesquirrell@gmail.com
PITTSBURGH, PA:
Pets Dx
Veterinary Imaging, Inc., 807 Camp Horne Road, Pittsburgh, PA 15237,
telephone 412-486-4800 and 412-348-2577.  See Akron, Ohio
entry above for details.
CHARLOTTETOWN, PE:
Atlantic Veterinary College at the
University of Prince Edward Island offers full MRI scans for $1,40000 CDN
(includes HST), blood work not included. Included are a pre-admission
neurology exam and full night recovery, radiology and neurology reports.
Website
avc.upei.ca
The CKCS Canada Club contact is
susan@wayfinderconsulting.ca
MT
PLEASANT, SC:
Dr.
Peter J. Brofman
, (ACVIM Neurology & Internal Medicine) and
Veterinary Specialty Care offer a reduced rate for MRIs for breeding
screening protocols only. The fee of $1000 includes the MRI and anesthesia
but pre-anesthetic blood work is not included. The MRI unit is a 1.5T magnet
and is available for screenings Monday through Friday. Veterinary Specialty
Care is located at 930 Pine Hollow Rd, Mt. Pleasant, SC 29464. You may
contact Dr. Brofman at 843-884-2441,
peterbrofman@gmail.com
, or
www.facebook.com/drpeterbrofman
PURCELLVILLE, VA
Pet MRI & Imaging Services, at Blue Ridge Veterinary Associates, 120 East
Cornwell Lane, Purcellville, VA 20132, offers CM/SM mini-scans for $975.00.
( Multiple dogs scanned the same day will be discounted).  The clinic has an
independent board-certified veterinary Neurologist available to read and
report the results to referring DVM within 24 hours. The price includes: IV
catheter, anesthesia (typically Propofol induction and inhalant isoflurane),
IV contrast, neuro-cranium MRI (multiple views to include sagittal,
transverse, dorsal weighted at T1/ T2, etc.), scan review and report by the
neurologist, and complete 1-on-1 patient monitoring thru recovery. The
owners should be prepared to leave their pets for 3 to 5 hours for
preparation, study, and recovery.  A report will be emailed to the owner and
referring veterinarian. Pre-anesthetic bloodwork (CBC CHEM) should be
performed within aprox. 2 weeks of the scan, and may be done by the owner's
regular veterinarian. If a patient needs a pre-anesthetic bloodwork panel,
the clinic can do so for an additional $98.00. If a patient needs
radiographs of the cervical region, those can be done for an additional
$95.00. Microchips may be deactivated by the magnet used in the scan.
Contact Christy Bell, CPC, LVT, at telephone 540-338-7387 (x104) or
703-606-8516 (work cell), email
contact@petmrimaging.com
or
Blueridgevets@aol.com
, website
www.PetMRimaging.com
UNITED KINGDOM:
See the list of MRI clinics on the website of The
Cavalier King Charles Spaniel Club at
www.thecavalierclub.co.uk/health/syringo/mriscan.html
NOTE: If you know of other MRI clinics offering reduced rate scans or
mini-scans for SM or CM, please let us know by emailing us at
Editor@CavalierHealth.org
RETURN TO TOP
DNA Testing
In a
March 2018 article
, a team of researchers from the UK and Canada
examined DNA samples from 65 cavalier King Charles spaniels and narrowed
down the likely potential "candidate" genes for CM/SM to PCDH17 in CFA22
(Canis Familiaris Autosome) and ZWINT in CFA26. They used MRI scans of
the craniums of affected and normal CKCS to compare size and shape
measurements of regions of the brains, to identify lines and angles
associated with sizes of syrinx diameters. The PCDH17 gene is involved
in the adhesion and sorting of cells in the brain and spinal cord during
tissue development. They speculate that the ZWINT gene may be related to
neuropathic pain, but this study did not detect any such association.
They conclude by calling for additional studies in larger numbers of
cavaliers and other affected brachycephalic breeds to investigate the
role of the two associated loci and the genes in the pathogenesis of
CM/SM.
RETURN TO TOP
Progression
SM is a progressive disease, but its progression can be is extremely variable.  Some
cavaliers initially may exhibit no scratching or pain; others tend to scratch with
only mild pain and no other neurological signs.  For some dogs, the
initial mild symptoms may never worsen.  Other CKCSs can be severely
disabled by pain and neurological signs within twelve months of the first
signs developing. As the SM syrinx enlarges, it may compress, and in some
cases destroy, the surrounding spinal cord tissue.
Chiari-like
malformation (CM) also has been found to be progressive in some cavaliers.
Interestingly, however, In a
January 2025 YouTube video
, Dr. Clare Rusbridge observed that as
CM-affected cavaliers grow older, their brains shrink, and as a
consequence, the severity of fhe CM -- and thus the resulting pain --
may reduce.
Dr. Rusbridge states in her
January 2024 YouTube video ("Surgical Options for Syringomyelia")
that
she has found that for most SM-affected dogs, the growth of the syrinx is
rapid at the start and once established, its size and shape remain stable
over time. She says that for most dogs, by their third year, they have the
biggest syrinx they are going to get.
Dr. Rusbridge stated in 2010, "In our experience, many cases of
syringomyelia are not progressive, especially if the syrinx is small."
In a
2011 study of 49
cavaliers
, the UK researchers found that "the severity of SM was
positively correlated with patient age. This is consistent with previous
studies indicating that CKCS with SM were significantly older than dogs
without SM (Couturier et al., 2008). It seems likely therefore, that SM is a
progressive disease in dogs."
Clinical statistics show that about 45% of affected
cavaliers develop signs of SM before their first birthday; another 40% will
show symptoms between ages one and four years; the 15% balance develop signs
later, with the oldest reported case of first developing symptoms at nearly
seven years of age.
In a
June 2011 study
of 555
cavaliers without any symptoms of syringomyelia, 25% of the one year old
dogs had SM and 70% of the dogs aged 6 years and older had SM.
In
an October 2012 study
by UK researchers of 48 cavaliers, nine of which
had only CM and the rest had both CM and SM, neuropathic pain progressed in
75% of the dogs over a mean average period of 39 months. The researchers
noted that it is not fully understood how CM/SM causes neuropathic pain, and
they did not make any such finding.
In
a November 2012 UK study
by a team of veteran CM/SM researchers of 12
cavalier King Charles spaniels with Chiari-like malformation, they found
that all of these conditions increased over time: syrinx width, height of
the foramen magnum, length of cerebellar herniation, and caudal cranial
fossa volume. The increase in the volume of the cranial fossa is believed to
be due to resorption of the supraoccipital bone as syringomyelia progresses.
They conclude: "We hypothesise that active resorption of the supraoccipital
bone occurs due to pressure from the cerebellum. These findings have
important implications for our understanding of the pathogenesis and
variable natural clinical progression of CM and syringomyelia in CKCS."
This study confirms a finding in
an October 2006 report
by Dr. Clare Rusbridge and Penny Knowler
that "on post-mortem examination, the supraoccipital bone overlying the
cerebellar vermis is remarkably thin and sometimes eroded so that the
foramen magnum is enlarged dorsally."
RETURN TO TOP
Treatment
Drugs
Physiotherapy --
hydrotherapy
Electomagnetic field
treatment (PEMF)
Alternative care
Surgery
Post-surgery soundwave therapy
The primary goal of treatment is to obtain relief from pain.  Treatment options consist of drugs and surgery, as are examined in detail
below.  Dr. Rusbridge has prepared a flow chart diagram of treatment options
(see below)
which she calls a
treatment algorithm
, which is
downloadable here in pdf format.
In summary, the first drug to administer, according to this Treatment
Algorithm's advice for dogs with either clinical signs of painful
Chiari-like malformation (CM-P) or phantom scratching, is
gabapentin
. For bad pain days, add either an
NSAID
or
paracetamol (Tylenol)
Corticosteriods
should be reserved as a
last resort and never as an initial treatment.
Dr. Rusbridge stated in 2010:
"In our experience, many cases of syringomyelia are not
progressive, especially if the syrinx is small, i.e. not every case with
this disease needs be managed surgically and many do well on medical
management, with drugs that reduce cerebrospinal fluid pressure (e.g.
antacids
such as
cimetidine
and
omeprazole
), non-steroidal anti-inflammatory drugs and adjuvant
analgesics such as
gabapentin
(see
Drugs, below
). When the surgery for this disease has questionable
long-term success it may be more appropriate to treat mild cases medically.
As a rule I rarely use corticosteroids when treating spinal cord disease."
RETURN TO TOP
Drugs
Anticonvulsants & their alternatives, for neuropathic pain
-- Gabapentin
-- Pregabalin
-- Other anticonvulsants
N-methyl-d-aspartate antagonists (NMDA)
Anitemetics
NSAIDs, for non-neuropathic pain from CM
Proton pump inhibitors
Antihistamines
Diuretics
Carbonic anhydrase inhibitors
Corticosteroids
Other drugs
Treatment
options for CM/SM are very limited.  The major means of treating
CM and SM in dogs is called "maintenance" and consists of
medicating the dog with drugs. There is no pharmaceutical
medication that can cure CM or SM. The most that can be hoped
for in using any of these prescription drugs is to attempt to
reduce any types of pain and other symptoms. This is called
"palliative care" and "suppressive care".
First of all, it is important to distinguish SM with symptoms
from SM without symptoms. As a general rule, SM without symptoms
(asymptomatic) should not be treated with drugs. Some medications
have been effective in some cases were the affected dog shows signs
of pain. Neurologists may start treatment with high doses of the
drug(s) and then gradually reduce the dosage to the lowest dose
which appears able to maintain remission of the symptoms.
(The two photos to the right above are
of the same cavalier King Charles spaniel. The photo on the left
shows the contorted face of a dog in severe pain. It was taken
before oral medication was administered. The photo at the right
shows the same dog, after oral medication has taken effect.)
• Anticonvulsants & their alternatives, for neuropathic pain
Anticonvulsants (antiepileptic)
, such as
gabapentin
and
pregabalin
, have been successful in
relieving
neuropathic pain, which is evidenced by behaviors such as
sensitivity to touch or phantom scratching.
-- Gabapentin
Gabapentin (Neurontin, Gabarone)
is an
anticonvulsant  which works through a
receptor on the membranes of brain and peripheral nerve cells.  It
binds to calcium channels and modulates calcium influx as well as
influences GABergic neurotransmission and prevents release of
glutamate,the neurotransmitter of pain.  Its effect is to deaden the irritated nerve
impulses in the dog's neck. In humans, gabapentin reportedly does not
interact with any other medications, and it is not metabolized, so it is
fully excreted in the urine and has no affect upon the liver. However, in
dogs, gabapentin is partially metabolized in the liver, and therefore the
prescribing neurologist may be expected to order periodic blood tests to
check the liver enzymes.
Dr. Rusbridge provides a detailed discussion of gabapentin on her
YouTube channel at this link
In an
April 2019 abstract
, UK researchers examined the records of 1,415
dogs treated with gabapentin in 2016 for a variety of conditions,
including 4.7% for CM/SM. Overall, it was reported to improve clinical
signs in 47.3% of the dogs. Most treatments were short-term, with 60%
treated for less than a month. The prevalence of suspected adverse
reactions was 7.85%, with the most common being sedation (5,2%) and
ataxia (1.3%).
In human studies, gabapentin has caused side effects, including
sleepiness, dizziness, and leg edema, which were minimized by increasing the
dose gradually and by taking the drug with food. In dogs, they may include
dose dependant effects, including sedation or drowsiness and recuction in
activity. Others may include mild ataxia (loss of coordination) and
increased appetite and weight gain. Rare ones include
myoclonus and other forms of seizures, vomiting, and diarrhea.
WARNING:
Beware of liquid
formulations of gabapentin, which may include the sweetener
xylitol
which is known to cause profound hypoglycemia and hepatic necrosis in dogs.
The most effective dosage range for Gabapentin is between 10 and 20
mg/kg, starting low, every 8 hours, to maintain effectiveness. Its peak
effectiveness is between 1 and 2 hours after the dose. Gabapentin  also may be given in combination with NSAIDs.
It has been recommended that gabapentin be dosed once every 8 hours, as it
lasts in the systems of most cavaliers that long. Gabapentin is commercially
manufactured in no less than a 100 mg. capsule. If the dog is prescribed a
lower dose than 100 mg and the capsule cannot be split or halved, the drug
may have to be specially prepared by a compounding pharmacy.
Gabapentin is not a fast acting medication, taking time to produce
results. Also, it may cause ataxia -- loss of coordination of muscular
movements.
In an
August 2020 article
, a team of Colorado State University researchers studied the treatment records of 240 dogs suffering chronic pain due to
a variety of diagnosed causes, including osteoarthritis (84.6%),
generalized, nonspecific back pain (9.2%), intervertebral disk disease
(7.5%), degenerative myelopathy (4.6%), and 56.67% not having a
definitive anatomical cause for their pain. None of the dogs had been
diagnosed with either Chiari-like malformation or syringomyelia. They
report finding that:
"The results from this case series suggest that gabapentin is
well-tolerated at much higher doses than what is typically prescribed.
Side effects were uncommon, with no clear pattern based on dose, or dog
size or age. Therefore, like many other analgesic medications, the
efficacy of gabapentin appears patient-specific and should be dosed to
effect until side effects are noted or analgesia is achieved."
In a
January 2025 YouTube video
, Dr. Clare Rusbridge observed that as
CM-affected cavaliers grow older, their brains shrink, and as a
consequence, the severity of fhe CM -- and thus the resulting pain --
may reduce. Therefore, she advises that the dosages of gabapentin be
reviewed periodically in older patients to determine if they need a dose
reduction.
RETURN TO TOP
-- Pregabalin
Another anticonvulsant,
pregabalin (Lyrica, Accord, Alzain, Lecaent,
Milpharm, Prekind, Rewisca, Sandoz, Zentiva)
, may be prescribed in treating CM/SM once high doses of gabapentin no longer are
effective.  Pregabalin is about five times more potent than gabapentin and
therefore achieves its effect at
lower doses (meaning, higher bioavailability).  Doses of pregabalin also reportedly  have a longer
lasting effect than gabapentin. Also, there is no need for a "wash out
period" between ending the gabapentin and starting the pregabalin. The
starting dose of pregabalin usually is about half the dosage of
gabapentin. Some neurologists may skip prescribing gabapentin and start
treating with pregabalin (at 4 to 5 mg/kg, twice a day). Pregabalin
should have less effect upon the liver than gabapentin, as it is
excreted mainly by the kidneys.
In a
May 2016 study
of six brands of pregabalin, the researchers found that "all
brands are pharmaceutically equivalent in their quality aspects." They
concluded that the lower cost brands of pregabalin could be used to treat
epilepsy. The rearchers do not identify the names of the six brands of
pregabalin.
In a
July 2019 article
a team of UK researchers
divided eight CM/SM-affected, symptomatic cavaliers
into two groups -- one administered pregabalin and the other with
placebo -- over 10 to 18 days and compared the results using owner
questionaire susing a numerical rating scale for pain, quantitative
sensory testing, cold latency, and blood samples. They report finding
that pregabalin-treated dogs showed:
•  improved owner-recorded daily pain scores using a
numerical rating scale;
•  improved mechanical
hyperalgesia (measured sensitivity to pain);
•  longer cold tolerance on
the neck and humeri.
They concluded that, "Pregabalin was
efficacious for the treatment of neuropathic pain caused by Chiari-like
malformation and syringomyelia in dogs."
In a
November 2019 article
, a team of Danish veterinary researchers report on their study of the effects of pregabalin
treatment upon 12 cavaliers  diagnosed with CM/SM and displaying
scratching episodes. The
cavaliers were aged from 1 to 7+ years. they were divided into two
groups, pregabalin and placebo, and they were treated over a period of
25 days, then no treatment for 2 days, then switched treatment for
another 25 days, so that both groups eventually were treated and
placebo. They determined the results of the treatment by observing the
number of scratching events during 10 minutes of physical activity. They
report finding an average of 84% (from 75% to 89%) reduction in the
number of scratching events relative to the baseline when compared to
the placebo. The dogs' owners assessed the quality of life after
treatment as "good" or "could not be better" in 6 of 11 dogs and
improved in 4 of 11 dogs. The most prevalent adverse events were
increased appetite in 9 of all 12 dogs and transient ataxia (lack of
some muscle control) in 9 of the 12 dogs. The researchers concluded
that:
"Pregabalin is superior to placebo in the reduction of clinical
signs of syringomyelia-related central neuropathic pain in dogs. At a
dose range of 13-19 mg kg-1 orally twice daily the encountered adverse
events were acceptable to all but one owner."
Dr. Rusbridge provides a detailed discussion of pregabalin on her
YouTube channel at this link
In a
January 2025 YouTube video
, Dr. Rusbridge observed that as
CM-affected cavaliers grow older, their brains shrink, and as a
consequence, the severity of fhe CM -- and thus the resulting pain --
may reduce. Therefore, she advises that the dosages of pregabalin be
reviewed periodically in older patients to determine if they need a dose
reduction
RETURN TO TOP
-- Other anitconvulsants
Paracetamol (acetaminophen, APAP, Tylenol)
is another pain
reliever, which is a convenient (in most dog owners' medicine cabinets)
medication for headaches due to CM. Its mechanism of action is not known. While it is rarely
prescribed for dogs, it can be quite useful when appropriately dosed. In large doses, paracetamol can be toxic to dogs'
livers.
Topiramate (Topamax)
is another anticonvulsant
medication which may be prescribed. However, in an
August 2015 study
, researchers found that no significant
quality-of-life difference was observed when cavaliers were treated with
either gabapentin or
topiramate (Topamax)
. They also
found that their data suggested that the addition of either of these two
drugs to dosing of the NSAID
carprofen
(Rimadyl, Quellin, Vetprofen
may be more effective than carprofen
alone. Dr. Rusbridge provides a detailed discussion of topiramate on her
YouTube channel at this link
and
at
this link
Amitriptyline (Elavil, Tryptizol, Laroxyl, Sarotex)
is a
tricyclic antidepressant (TCA)
by Merck which may be prescribed as an
alternative to either gabapentin or pregabalin. In a
January 2009 case study
of three dogs (none CKCSs), the clinicians
report that, "Treatment with the tricyclic antidepressant drug,
amitriptyline, or the antiepileptic drug, gabapentin, resulted in either a
dramatic improvement or full resolution of clinical signs in all cases." See
Dr.
Rusbridge's YouTube
video on this drug.
Zonisamide (Zonegram)
is an anticonvulsant which in clinical
trials appears to be effective for generalized seizures in dogs. It's
anti-seizure effect is believed to work through sodium and calcium channels.
Dr. Curtis Dewey
has conducted studies of this drug.
Levetiracetam (Keppra)
is an anticonvulsant which
can also be used in conjunction with phenobarbital and/or potassium bromide.
It appears to be relatively safe for dogs, and reportedly rarely has any
adverse side effects and does not appear to affect the liver or liver
enzymes.
Oral opioids (pethidine, methadone, tramadol)
are
alternatives to anticonvulsants. However, there is little evidence of their
effectiveness for acute pain in dogs.
Methylsulfonyl-methane (MSM)
is recommended by some veterinary neurologists as a dietary supplement.
RETURN TO TOP
--
N-methyl-d-aspartate antagonists (NMDA)
Amantadine (Endantadine, Gocovri, Osmolex ER, Symmetrel)
is an N-methyl-d-aspartate antagonist (NMDA), which is used for control of the symptoms of Parkinson's disease in humans,
together with gabapentin or pregabalin. Amantadine is believed to release
brain dopamine from nerve endings making it more available to activate
dopaminergic receptors. See this
January 2008 article
, in which the researchers found clinical
improvement in dogs with chronic osteoarthritis pain when amantadine was
used in combination with meloxicam. See
Dr.
Rusbridge's YouTube
video on this drug.
Ketamine (Ketalar)
is an intravenous or subcutaneously
injected NMDA used as an
induction and maintenance agent for sedation and to provide general
anesthesia. It is being used more frequently in treating CM/SM dogs
which no longer respond to gabapentin and pregabalin. It blocks sensory
perception in humans. It is administered intraveneously in low doses and
infrequently to dogs for CM. It also provides pain relief and controls symptoms of
epilepsy,
depression, and suicidal thoughts. See
Dr. Rusbridge's YouTube
video on this drug.
Memantidine (Axura, Ebixa, Namenda)
is another NMDA, which is used to treat advanced stages of Alzheimer's
disease. See
Dr. Rusbridge's YouTube
video on this drug.
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--
Antiemetics
Maropitant citrate (Cerenia)
is licensed to prevent motion
sickness and vomiting (an antiemetic), especially for dogs receiving
chemotherapy. Some veterinarians have prescribed it to treat symptomatic
syringomyelia, especially phantom scratching. Dr. Rusbridge added
maropitant to her CM/SM Treatment Algorithm in 2021 for
initial treatment of
phantom scratching
. Maropitant is an
antagonist for the neurokinin (NK1) receptor Substance P, which is
present in the dorsal root ganglia and spinal cord dorsal horn.
Dr. Rusbridge says that "Maropitant is amazingly effective at stopping
the [phantom] scratching, but the bad news is you can't give it
continuously. If you give it continuously, the effect stops. ... I give
the owner the box of four tablets for bad scratching days. ... If they
are having a particularly bad day, then it may be used then."
In
an April 2013 study
of 26 cavaliers, German researchers found "an
association" between pain and SM asymmetry, and they found "a strong
association" between pain and dorsal horn involvement of SM. The
researchers conclude that the release of interleukin-6 and substance P
is a factor in the development of persistent pain in cavaliers with SM.
They suggest that this information could offer new diagnostic and
treatment options for CKCSs with SM. An un-published 2021 study of
this drug has shown evidence of its safety and effectiveness.
In a
January 2021 abstract of a study
of
this drug treating 9 CM/SM-affected cavaliers, their
owners reported that the frequency of phantom scratching had decreased
significantly, including spontaneous scratching, scratching while
walking, scratching when groomed, and scratching when touched.
See, also
Dr. Rusbridge's January 2024 YouTube video
on using maropitant for
treating phantom scratching.
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--
NSAIDs, for non-neuropathic pain from CM
The use of non-steroidal
anti-inflammatory drugs (
NSAIDs
), such as
carprofen
(Rimadyl, Quellin, Vetprofen
),
meloxicam (
Metacam
Loxicom), firocoxib (
Previcox
), mavacoxib (Trocoxil),
grapiprant (Galliprant),
and
aspirin
, may relieve the
symptoms of non-neuropathic pain, such as is caused by the Chiari-like
malformation (CM) rather than from the syringomyelia (SM), as evidenced by
yelping when either being picked up of changing posture. These drugs
do not retard deterioration due to progression of the SM.
*WARNING:
Carprofen
(Rimadyl, Quellin, Vetprofen)
may have serious side effects and should not be given without a
veterinarian's close guidance and monitoring. Also, carprofen, when
combined with
omeprazole
, may
negatively impact intestinal health. See
this September 2020 article
It has been reported that SM-affected
cavaliers have been found to have a high level of inflammatory proteins in
their bodies, and that for that reason, NSAIDs often provide some initial
relief from pain. Also,
doxycycline
, a tetracycline
antibiotic designed to treat bacterial infections, has been
prescribed to CM/SM patients as an anti-inflammatory similar to
NSAIDs. An alternative to doxycycline is
minocyclin
e,
which also is an antibiotic in the tetracycline family.
NSAIDs and other conventional analgesic medications have not been found
to be effective by themselves to relieve neuropathic pain. Two 2007 studies
(1)
(2)
show that the type of pain
behavior suggests that the dogs experience neuropathic pain, probably due to
disordered neural processing in the damaged dorsal horn, and that, "as such
it is likely that conventional analgesic medication may be ineffective."
NSAIDs should not be administered without supervision by a
veterinarian. The US Food & Drug Administration (FDA) warns about
the dangers of using NSAIDs
here on its website
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--
Proton pump inhibitors
Drugs which reduce the production of cerebrospinal fluid, including
proton pump inhibitors
such as
omeprazole
Prilosec
Losec, Omesec,
Zegerid
and
Pantoprazole (Protonix)
are reported to be useful to reduce intracranial pressure. (See
this
April 1997 article
"We conclude that in the canine model, physiological doses of omeprazole
decrease CSF production by about 26.") However, in a
March 2016 article
, researchers reported that, "There was no evidence of
an effect of omeprazole on CSF production in healthy dogs." However, in an
August 2019 article
, the same researchers questioned whether their use
of evaluating the albumen quotient (QAlb; ratio between CSF and serum
albumin concentration) was an appropriate marker. So, the jury remains out
on the effectiveness of omeprazole, but anecdotally, a positive response to
omeprazole has been  reported. See Dr. Rusbridge's
June 2020 article
. Dr. Rusbridge also provides a detailed discussion of
omeprazole on her
YouTube channel at this link
Long term
use of omeprazole is not recommended by some neurologists, as its long term
use reportedly has increased the risk of stomach
cancer in lab rats. Short term use reportedly can cause a "profound and sustained
increase in serum gastrin concentration in dogs."
See June 2011 report
As a
proton-pump inhibitor, omeprazole inhibits some cytochrome
P450 enzymes in humans (primarily CYP2C19) and may inhibit the clearance of
some drugs, including diazepam, midazolam, warfarin, and carbamazepine.
Omeprazole also reportedly impairs conversion of clopidogrel, an
antiplatelet agent, to its active metabolite in humans, leading to decreased
antiplatelet efficacy and increased risk for ischemic cardiac events.
Omeprazole may also lead to digoxin toxicosis, possibly via inhibition of
P-glycoprotein efflux of digoxin. See this
June 2013 report
. When combined with
carprofen
omeprazole may negatively impact intestinal health, according to
this September 2020 article
As a potent inhibitor of gastric acid secretion, all proton pump blockers
can decrease the absorption of compounds that require an acidic pH for
optimal absorption, including iron supplements, oral zinc, ketoconazole, and
itraconazole. This same interaction also applies to H2-blockers (e.g.,
Pepcid AC
[famotidine]
). Discontinuing antacids when ketoconazole or itraconazole is
being given may be advisable. Alternatively, if antacids cannot be
discontinued, fluconazole can be considered if indicated, as fluconazole
absorption is not affected by changes in gastric pH.
See this
June 2013 report
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--
Antihistamines
Neurologists have been prescribing
cimetidine
Tagamet
Zitac),
which is a
histamine H2-receptor antagonist --
an
antihistamine
.  Histamine contributes to inflammation
and  causes  smooth muscles  to constrict.  Cimetidine
is diffused into the cerebrospinal fluid and reportedly may contribute to
reducing the flow of CSF.  When taken with gabapentin, cimetidine also
reportedly may increase the amount of gabapentin in the blood by decreasing
its elimination.  Therefore, when taken together, the dosages may
require adjustment.
Cimetidine is a potent inhibitor of several families of cytochrome P450
enzymes and can also inhibit transporter pumps and decrease the renal
excretion of some drugs, including clearance of many drugs, such as
theophylline, lidocaine, midazolam, and propranolol.
See this
June 2013 report
Dr. Rusbridge provides a detailed discussion of cimetidine on her
YouTube channel at this link
Another H2-blocker occasionally prescribed is
famotidine
Pepcid AC
).
Dr. Rusbridge provides a detailed discussion of famotidine on her
YouTube channel at this link
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--
Diuretics
Diuretics
furosemide
(Lasix,
Diuride, Frudix, Frusemide)
and
spironolactone
(Aldactone)
also
reduce the production of cerebrospinal fluid
and
are reported to be useful to reduce intracranial pressure and to
slow the progression in the size of the SM ysrinxes. Diuretics are being used infrequently, due to side effects and the success
of other CSF pressure reducers. Dr. Rusbridge provides a detailed discussion
of furosemide on her
YouTube channel at this link
In an
April 2016 article
a UK veterinary neurologist reported
studying the effect of furosemide therapy upon the progression of syrinx
growth in seven cavalier King Charles spaniels. He stated:
"In all seven dogs, syrinx width and length increased at the
follow-up MRI and in four cases a new syrinx had developed (Table 1).
Furosemide did not prevent further syrinx expansion nor reduce the size
of the syrinx but it remains unknown whether the medical treatment may
have delayed the inevitable expansion of the syrinx. Studies of a larger
population and prospective, randomised, blinded comparisons between
different treatments (medical, surgical, medical vs surgical) are needed
to ascertain which will produce the best clinical results."
In a
July 2025 study
of the progression of SM in Pomeranians, 12 of 45 of
them were treated with furosemide during the interval between their first
and second MRI scans. The researchers found that the increase in the
diameter of the SM at the time of their second MRI "was significantly
smaller in dogs treated with furosemide compared to those not treated."
Natural diuretics include
urea (
AC Carbamide
by
Standard Process
, and
Wu Ling San
by Mayway and
Alisma
by Seven Forests, both traditional Chinese herbal medicines (TCM).
Holistic supplements should be taken only if prescribed by a licensed
veterinarian who also is holistically trained in TCM. Search webpages for
finding holistic veterinarians  in the United States and Canada are
located
here
and in the United Kingdom,
here
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--
Carbonic anhydrase
inhibitors
Carbonic anhydrase inhibitors,
such as
acetazolamide (Diamox)
also serve to
decrease the flow of
cerebrospinal fluid,
but their adverse side effects of abdominal pain,
lethargy, weakness, and bone marrow suppression limit long term use. Dr.
Rusbridge provides a detailed discussion of acetazolamide on her
YouTube channel at this link
Methazolamide (Glauctabs, MZM, Neptazane)
, also is a carbonic
anhydrase inhibitor. Carbonic anhydrase is a protein which can affect fluid
production in various parts of the body.  Methazolamide reduces the
activity of this protein. It's initial use was to treat glaucoma by reducing
the amount of fluid produced in the eyes and therefore also reducing
pressure in the eye.
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--
Corticosteroids
Before the disease progresses to its severe form, the use of
anti-inflammatory
corticosteroids
, such as
prednisolone
(Prelone,
Prednidale),
methyl-prednisolone (Medrol, Medrone),
and
dexamethasone (Decadron,
Dexamethasone Intensol, Dexone, Hexadrol)
, may relieve the
symptoms but not the deterioration.  As a general rule, corticosteroids
should be reserved for a last resort, although some neurologists
will start initial treatment of symptomatic dogs with a combination
of an anticonvulsants, such as gabapentin, and a none-inflammatory
corticosteroid. However, dogs should
never
be treated with both a cortisteroid and an NSAID at the same time. See this
March 2011 report
All that said, however, Dr. Rusbridge stated in
July 2024
that she is least likely to use steroids, and, "some
dogs come on steroids to my clinic, and the first thing we do is remove
the steroids, and the dogs are much better for it." In an
April 2025
YouTube video
, Dr. Rusbridge said (at 49:31 minutes):
"At the current time, I see hundreds and hundreds and hundreds of
dogs with Chiari-malformation and syringomyelia. I only have two dogs
that are receiving corticosteroids, and both of those dogs, the
corticosteroids are not helping those dogs, and the main challenge is to
get both of those dogs off of the corticosteroids. And in both
instances, those dogs are having to use ketamine to help reduce the
dogs' pain to allow us to reduce the corticosteroids.
Please do
not blanket treat these dogs with corticosteroids! You are doing more
harm than good. And I can't overstate that enough!
Corticosteroids have serious side effects,
such as weight, gait, and skin changes, harmful suppression of the
immune system, and
iatrogenic hyperadrenocorticism
(Cushing's disease)
.  Long term use of these drugs is not advised. Dr.
Rusbridge provides a detailed discussion of corticosteroids on her
YouTube channel at this link
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--
Other drugs
Oclacitinib (Apoquel):
In a
June
2017 article
, a German internal medicine specialist treated two cavalier King Charles spaniels with the main symptom of
"nonspecific itching", both diagnosed by MRI to have Chiari-like
malformation and syringomyelia, with
oclacitinib (Apoquel)
, a selective
inhibitor of janus kinase (JAK1 and JAK3) enzymes, which are proteins
involved in signaling a pathway that results in itching and
inflammation. She stated that, in the case of allergic dermatitis,
oclacitinib inhibits itching in the neurological range. She reported:
"In the two Cavalier King Charles Spaniels presented, a therapy with
oclacitinib was initiated in the standard dose, which is recommended for
atopic dermatitis (0.4-0.6 mg / kg 2 × daily for 14 days, then 1 × daily
administration). ... Result and conclusion: After only 2 days the
itching is clearly reduced, no scratching behavior can be observed after
1 week and the owners report a generally improved general condition.
Both patients are taking the drug for a year now and are clinically
inconspicuous, side effects have not occurred."
Melatonin
is a hormone produced by the
pineal gland in the brain. Melatonin supplement has been prescribed by
veterinarians to ease anxiety and restlessness in dogs. Some vets also have
prescribed it for dogs with SM symptoms. Since melatonin is a hormone, it
should not be given to dogs without the advice of a veterinarian. Melatonin
can have adverse side effects, and in particular, it is contraindicated for
dogs that are pregnant or lactating.
Maropitant citrate (Cerenia)
is licensed to prevent motion
sickness and vomiting (an antiemetic), especially for dogs receiving
chemotherapy. Some veterinarians have prescribed it to treat symptomatic
syringomyelia, especially phantom scratching. Dr. Rusbridge added
maropitant to her CM/SM Treatment Algorithm in 2021 for initial
treatment of phantom scratching. Maropitant is an
antagonist for the neurokinin (NK1) receptor Substance P, which is
present in the dorsal root ganglia and spinal cord dorsal horn. In
an April 2013 study
of 26 cavaliers, German researchers found "an
association" between pain and SM asymmetry, and they found "a strong
association" between pain and dorsal horn involvement of SM. The
researchers conclude that the release of interleukin-6 and substance P
is a factor in the development of persistent pain in cavaliers with SM.
They suggest that this information could offer new diagnostic and
treatment options for CKCSs with SM.  An un-published study of this
drug has shown evidence of its safety and effectiveness. However, no studies of
treating SM-affected dogs with Cerenia have been published.
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Physiotherapy -- hydrotherapy
Physiotherapy, particularly hydrotherapy
(right)
, has been found to be the
best form of treatment for scoliosis and other gait abnormalities. The
goal is to mazimize their musculature to enable the affected dogs to best
compensate for the progression of CM/SM. Surgery is the back up option
for treating this category of symtomatic dogs.
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Electomagnetic field
treatment (PEMF)
-- Assisi Loop
Targeted pulsed electromagnetic field (PEMF)
treatments have been studied and used on dogs
following decompressive
spinal surgery. A device which creates a pulsed electromagnetic field is
placed near the affected area of the dog's body produces a small,
localized electrical field surrounding the dog's affected, inflammed
tissues. This reportedly increases calcium binding by calmodulin, which
binds to constitutive nitric oxide synthase (cNOS), producing nitric
oxide (NO) with a vasodilatory effect encouraging blood-flow, and
limiting inflammation, and increasing bone growth and repair. Recently,
this device also has been used with some reported anecdotal success in
treating pain in CM/SM dogs.
In an
August 2018 article
, North Carolina State veterinary school
researchers reported
that a loop PEMF device resulted in evidence of
reduced incision-associated pain in post-IVDD-surgeries and may also
have reduced the extent of spinal cord injury and enhanced gait and
movement function. In November 2018, NC State University's  board
certified veterinary neurologist Dr. Natasha Olby commenced a study of
cavaliers diagnosed with CM/SM and exhibiting signs of pain and phantom
scratching for the effect of PEMF treatments to control the pain and
itching sensations. The treatments were to be delivered in the form of a
PEMF loop
(see image above at left)
for a period of two months.  The loop is marketed
as the
Assisi Loop
to veterinarians and pharmacists.
See this
YouTube video
about the Assisi Loop treating a cavalier, Madison
(right)
, diagnosed with CM/SM. For more
information, see the
Assisi
Animal Health website
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Alternative care
Cannabinol (CBD oil)
Nerve Eight (8)
Palmitoylethanolamide
(PEA)
Acupuncture
Laser therapy
Various types of what are called "complementary therapies" are helpful to
affected dogs, particularly to relieve pain. In addition to
hydrotherapy
and the
Assisi Loop
mentioned
above and those treatments listed below in this section, choices include
gentle massage
and
transcutaneous electrical nerve stimulation (TENS)
-- a small device that
delivers the current at or near your nerves to block or change your
perception of pain, and
ultrasound
therapy
. However, spinal manipulation, such as by chiropractic, is not
appropriate for CM/SM patients, warns Dr. Clare Rusbridge.
Holistic supplements should be taken only if prescribed by a licensed
veterinarian who also is holistically trained. Search webpages for finding
holistic veterinarians in the United States are located
here
and
here
--
Cannabinol (CBD oil)
There are no published research articles focused upon
cannabinol (CBD)
treating
neuropathic pain. Nontheless, veterinary neurologists have considered
the possible value of CBD products in treating forms of neuropathic
pain, including pain due to Chiari-like malformation and/or
syringomyelia. CBD oil might have some use for managing pain through the
cannabinoid CB2 receptors, according to veterinary neurologist Dr. Clare
Rusbrige.
Dr. Rusbridge states in her
December 2023 YouTube video "Cannabinol (CBD oil) and neuropathic pain
in animals"
that it is difficult for her to recommend CBD oil for
her patients because:
• What is an effective and safe dose for neuropathic pain?
It appears to require a very high dose to compensate for pain.
Concerns about safety, especially if combined with other medication or
given life long. High doses or long term treatement will induce liver
enzymes, requiring liver function to be monitored frequently.
• Can be tricky for vets to source and prescribe a
legal preparation.
Cannabinol (CBD) is
is a
cannabinoid compound
produced from hemp and marijuana (Cannabis
Sativa) plants. CBD oil mimics the endocannabinoid molecules which the
dog's (and our) body produces in several different organs. They play
roles in reducing pain, regulating inflammation, and affecting the
immune system, by initially binding to receptors in the brain.
CBD is non-psychoactive, unlike
tetrahydrocannabinol (THC
),
another cannabinoid compound from marijuana, which is considered
psychoactive by altering the mental state, and can be highly toxic to
dogs.
Varieties of CBD
: Cannabidiol-based veterinary products are derived
mainly from hemp (
Cannabis sativa
) and must contain less than 0.3%
tetrahydrocannabinol (THC). This form of CBD can be processed into "full
spectrum" or "broad spectrum" and also may be in the form of a
"distillate", in which all THC has been removed, or in the form of CBD
"isolate", which is a purifed powder.
Full Spectrum:
Full spectrum CBD contains other extracts found in the
cannabis plant, including terpenes, and up to 0.3% THC.
Broad
Spectrum:
Broad spectrum CBD also contains some other cannabis compounds
but no more than trace amounts of THC.
CBD Isolate:
CBD isolate
is pure CBD and contains no other cannabis plant compounds.
Naked CBD:
Naked CBD describes CBD oil by itself,
as opposed to being capsultated or microcapsulated or combined with
any other substance, such as deoxycholic acid (DCA).
Liposomal CBD
This is an orally administered encapsultated CBD which is packaged
within liposomes, small fatty cellular sacs which improve
bioavailability of the CBD by enabling it to be withstand digesstion
in the stomach and degradation in the liver. Lipsomal CBD was tested
on dogs in this
September 2020 article
Cannabidiolic acid
(CBDA)
is an a cid precursor of CBD. It forms CBD when
heated. It has been shown in some studies to be more potent that CBD
for treating rats. It has been found to be more readily absorbed
into the human bloodstream than CBD. Aa theory is that adding CBDA
to doses of CBD may make the CBD more absorbable. In this
September 2020 article
, the investigators found that CBDA is
absorbed at least twice as well as CBD in dogs within a 24 hour
period, with some differences depending upon the medium used to
deliver the oral treatment.
The only three classifications of canine disorders for which there
have been any published clinical studies are: osteoarthritis, idiopathic
epilepsy, and atopic dermatitis. Even those studies have included very
few dogs, including as few as 4 dogs for each category of CBD or
placebo, and for very short study times. None of these studies rank
above "pilot studies".
There are no published research articles focused upon CBD treating
neuropathic pain. Nontheless, veterinary neurologists have considered
the possible value of CBD products in treating forms of neuropathic
pain, including pain due to Chiari-like malformation and/or
syringomyelia. CBD oil might have some use for managing pain through the
cannabinoid CB2 receptors, according to veterinary neurologist Dr. Clare
Rusbrige.
See our
Cannabis webpage
for
additional details about CBD, including delivery methods,
bioavailability, dosages, and adverse reactions.
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--
Nerve Eight (8)
An herbal supplement which cavalier owners report calms dogs suffering
from the symptomatic scratching of SM is a product called
"Nerve
Eight" or "Nerve 8"
manufactured by Nature's Sunshine of Provo, Utah
(left)
, which consists of white willow
bark (salix alba),
black cohosh root (cimicifuga racemosa), capsicum fruit (capsicum annuum),
valerian root (Valeriana officinalis), ginger root (zingiber officinale),
hops flowers (humulus lupulus), wood betony herb (betonica officinalis), and
devil's claw root (harpago-phytum procumbens).
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--
Palmitoylethanolamide (PEA)
Palmitoylethanolamide (PEA) is a
N-acylethanolamine molecule
in a family of long-chain fatty acid
amides
called
ALIAmides
. PEA has been found in rat and mice studies to limit
hyperactvity in immune cells and thereby control inflammatory responses
and resulting tissue damage. PEA is produced by the animal's body as
needed in response to certain types of injuries. PEA is a product of
normal fatty acid synthesis from palmitic acid. It is found in many
common foods, particularly palm oil, soy beans, egg yolks, and peanuts.
The commercial version is most commonly manufactured from palm oil
. While no
objective, unbiased clinical studies of the
effect of PEA on treating CM or SM have been published, one
under-powered pilot study, the
April 2011 Normast Study
, does exist, and some
veterinarians reportedly are treating these disorders for pain with PEA,
with mixed results.
Not all PEA is alike
. There are three types of PEA.
Basic PEA
, called
"naive PEA"
is almost totally insoluble in water and under gastrointestinal
conditions  and therefore the oral intake of it (rather than
being injected directly into the abdomen) has very poor bioavailability,
meaning that it does not get absorbed well in the dog's gut. S
ee
this
May 2021 article
and this
July 2025 article
Micronized PEA
(m-PEA or micro-palmitoylethanolamide) is a patented technique that
reduces the diameter of PEA particles, making them absorbable in
the intestine, which
has been found to be more effective than ordinary basic PEA in
activating PEA levels in blood plasma in dogs.
See this
August 2014 article
Ultra-micronized PEA
(um-PEA), also patented, reduces the PEA
particle size further, to enable it to cross the blood-brain
barrier, likewise has been found to be much more
effective than basic PEA.  See this
August 2014 article
• Water-Dispersible PEA
(PEA-WD), also
patented, reduces the PEA to a powder which can be dispersed in cold
water. It has been found to be 16 times more effective than basic
PEA. See this
July 2025 article
PEA+LipiSperse
(Levagen)
is a combination of PEA and a delivery system designed to overcome
PEA's poor bioavailability. LipiSperse is a mixture of surfactants,
polar lipids, and solvents which enable the PEA to disperse in
water. See this
July 2018 article
and this
2020 article
for details about LipiSperse.
• Hybrid versions of PEA:
Additonally, PEA has been combined with other ingredients and used
in some published studies. These include FenuMat-PEA (P-fen), which
is a PEA hybrid combined with the herb fenugreek (trigonella
foenum-graecum), and hybrids combined with resveratrol,
quercetin
fisstin, daidzein, genistein, and boswellic acid. See this
September 2024 article
and this
May 2025 article
and this
July 2025 article
In an
August 2014 study
comparing the 3 versions of PEA -- basic,
micronized, and ultra-micronized -- in treating rats for inflammatory
pain, the researchers reported that the pain "parameters were
significantly decreased by oral treatment with micronized PEA-m and
ultramicronized PEA-um at each time point compared to nonmicronized
PeaPure."
In a
July 2025 article
. the researchers compared the dissolution rate and
bioavailability of basic PEA and water-dispersible PEA (PEA-WD )and
reported finding that PEA-WD was 16 times more effective than basic PEA.
PEA micronization and ultra-micronization are patented (by Italian
company,  EPITECH
Group SpA) processing techniques that reduce the diameter of the PEA
particle to a micronized or ultra-micronized size
which optimizes the
PEA's absorbability along the intestine. Micronization increases the
drug's surface area, thereby improving its dissolution rate and
minimizing its absorption difficulties. The ultra-micronized size
also enables
the PEA to cross the blood-brain barrier. See this
February 2021
article
If a PEA product is not advertised as being
micronized
or
ultra-micronized
(or
water-dispersible
), then
Dr. Clare Rusbridge advises
that
"You
probably are wasting your money."
A variety of brands of
micronized and ultra-micronized PEA are offered on-line.
Recent research has produced evidence that ALIAmides can relieve dogs
with hypersensitive skin disorders. In an
August 2015 article
, Italian researchers conducted an 8-week study
of the effectiveness of oral
ultra-micronized palmitoylethanolamide
(um-PEA)
in 160 dogs with moderate atopic dermatitis. Each dog received
a daily dose of um-PEA at the rate of 10 mg/kg for 56 days. They report
finding that um-PEA appeared to be effective and safe in reducing
pruritus and skin lesions, and in improving the quality of life in dogs
with moderate atopic dermatitis and moderate pruritus.
As for dosages, the studies using micronized PEA, the range was from
10 to 15 mg/kg/day, and the range for ultra-micronized was 24 mg/kg
(for osteoarthritis).
Read more about PEA on our
PEA webpage
Palm oil: The palm oil cultivation industry has been destroying
rainforests in Sumatra and Borneo in Indonesia and Malaysia, the only
habitats of orangutans. If you are going to obtain PEA, we suggest that
you do so only from vendors whose PEA has been manufactured with palm
oil from sustainable sources and not the deforestation of rainforests.
This link
connects to a "PalmOil Scan Mobile App"
which will enable you to
determine if the PEA vendors you select obtain their palm oil from
sustainable sources.
RETURN TO TOP
• Acupuncture
In a
September 2016 article
, a UK veterinarian reported on the successful use
of
acupuncture
(photo at right)
to control the
signs of pain in a cavalier King Charles spaniel suffering from Chiari-like
malformation and
"This patient exhibited signs which suggested it was also suffering
from headaches. It often presented with a frowning expression and during
these times intensely disliked being touched, rubbed or patted on the
head. Acupuncture had a definite positive effect on this patient with
reductions in all the signs including the signs of phantom scratching
and vocalisation."
Dr. Curtis Dewey,
neurologist at Cornell University, is conducting a study (2019-2020) to evaluate the
effectiveness of acupuncture treatments on the thermal patterns in the
cervical region of cavalier King Charles spaniels with Chiari-like
malformation (CM) and syringomyelia. Ten CKCSs will be in each of three
groups -- one treated with dry needling acupuncture, one with
electro-acupunture, and the third a placebo group. Thermal images taken
before and after treatments will be compared. The dogs' owners will
also be asked to complete questionnaires. Details are on
this webpage.
Laser therapy
Cold laser therapy, including K-Laser (high power laser therapy) and
LZ30-z (frequency-specific low level laser therapy) has been used
anecdotally with some reports of successfully relieving signs of pain
and discomfort when applied periodically.
RETURN TO TOP
Surgery
Introduction
Foramen Magnum
Decompression (FMD)
Cranioplasty using titanium
Cranioplasty using LactoSorb SE mesh
Duraplasty using swine or bovine tissue
Duraplasty using only patient's fat tissue
Duraplasty using tissue adhesives
Syringosubarachnoid shunt
Ventriculoperitoneal shunt
Conclusion about surgeries
Introduction to Surgery
Surgery to allow the cerebrospinal fluid to flow normally may be
necessary to reduce the pain and deterioration. Surgery is directed
only at the Chiari-like malformation. It is not upon the syrinx,
although it should eliminate growth of the syrinx. Surgery is recommended
if there is significant pain or a deteriorating condition despite
medications and alternative therapies.
The current
threshold for surgery seems to consist of dogs with:  (1) MRI evidence
of Chiari-like malformation and cervical syringomyelia; (2) Syrinx in the
cervical spinal cord measuring >3mm diameter on transverse T2 MRI; nd (3)
Clinical signs of phantom scratching, cervical pain or hypersensitivity, or
thoracic limb paresis without MRI/CSF evidence of other changes that could
produce the same clinical signs.
Surgery usually
is successful in significantly reducing the Chiari-pain and improving the
neurological deficits.  However, surgery will not always reverse the
filling mechanism of the syrinx and cause it to collapse. The extent of
a successful outcome of a surgery is best determined by a post-operative
MRI scan at around six months.
Not all neurologists experienced with CM and SM in
cavaliers agree about when and if surgery should be performed. Some have found that early surgical treatment is more successful than
waiting and considering it as a last resort, and that the longer the dog has
been in pain, the less likely it will recover. However, others have observed
that SM will not continuously progress to a severe stage in all
SM-affected young dogs.
Dr. Andy Shores
of Mississippi State University has stated that, "Severely affected
patients with syrinxes <3mm in diameter that respond poorly to medical
management might also benefit from surgery."
The earliest reported surgeries to relieve CM was a series of suboccipital
craniectomies and cranial dorsal laminectomies by a team of Belgium
neurosurgeons in 2003. They had little success. Read
their report here
Terms which describe different types of surgical procedures include
craniectomy, cranioplasty, duraplasty, and insertion of a shunt:
Craniectomy
involves removing a portion of the
skull bone to relieve pressure. This procedure is common in most
surgeries treating CM/SM.
Cranioplasty
begins with a craniectomy, followed
by replacement of the removed portion of bone with a titanium or a
synthetic material. It includes
foramen magnum decompression
(FMD)
described below.
Duraplasty
is the name of a surgical procedure
which grafts a piece of fat or synthetic tissue to the portion of the
dog's dura (the fibrous membrane beneath the skull, which insulates the
brain and central nervous system), which must be cut during these
surgeries.
Shunt
is the insertion of a tube, usually
silicone, into the syrinx, to drain fluid from the area around the
syrinx and thereby reduce the size of the syrinx.
Dr. Rusbridge provides a detailed discussion of CM/SM surgery on her
YouTube channel at this link
RETURN TO TOP
• Foramen magnum
decompression (FMD)
The most common form of surgery is called
foramen magnum
decompression (FMD),
or
suboccipital decompression
or
cranial cervical decompression
, surgery.  The surgeon removes the
supraoccipital bone and the cranial dorsal laminae of the
atlas.
(See the decompression site over the occipital bone and foramen magnum,
outlined in diagram at right.)
Decompression surgery may include incising through the dura sac, a tough
membrane which contains the brain inside of the skull, and installing a
dural graft or shunt, to allow more space for the cerebellum and to reduce
the pressure of the flow of CSF.  In some surgeries, the entire
occipital bone also is removed.  All FMD surgeries are technically
difficult and should be performed only by experienced neurological surgeons.
Although this form of surgery often is successful
in relieving pain due to Chiari, it may be expensive,
and many dogs may either have a recurrence of the disease or still show
some signs of pain and phantom scratching.  Some
post-operative pain is only temporary, due to leakage of CSF through the
incision in the dura until that incision
heals, or because the syrinx is still present after the surgery. However,
medications which did not work prior to surgery may be more  successful
following it. Nevertheless, since phantom scratching is due to the SM syrinx
and not the Chiari-like malformation, it may be expected to continue
following this form of surgery.
The
most frequent reason for recurrence reportedly is the development of
post-operative scar tissue which compresses the cervicomedullary junction.
Scar tissue has required additional surgery to remove it in about 25%
of all FMD surgical cases. To avoid the development of scar tissue, it is
important to not allow the dog too much freedom of movement or excitement
during the healing process, which may last from three to six months.
In an effort to prevent such scar tissue from
re-compressing the junction, modified versions of FMD include
inserting
either a skull plate made of
titanium mesh
at the junction before closing
the incisions,
(see photo below)
, or covering the sutured dura with a tented graft
of swine intestine tissue, covered by a layer of the dog's fat tissue.
In a November 2025 article, Korean veterinary surgeons Sung Su Park,
Ji Young Park, and Ho Jae Han report the results on performing foramen
magnum decompression surgery on 87 small dogs (none being cavaliers)
diagnosed
with Chiari-like malformation and syringomyelia (CM/SM), using a
titanium mesh (TM) shaped with a gap between the surface of the
cerebellum. Their aim was to avoid the formation of post-operative scar
tissue due to the TM coming into contact with the cerebellum in dogs
with limited size of the occipital region. The TM plate they designed is
contoured to follow the occipital curvature, with a decompression gap
over the cerebellum and also avoiding contact with the dorsal arch of
the first cervical vertebra.
(See photograph.)
A total of 76
dogs (87%) showed long-term improvement, with no follow-up surgeries
required. A subset of 11 dogs (13%) required continued medication after
surgery due to the recurrence of signs. They concluded that:
"Retrospective analysis showed that the modified TM technique, using a
deliberate gap, was safe and effective in small-breed dogs with CM/SM,
successfully preserving the decompression space and maintaining
long-term neurologic stability."
Decompression surgery is not expected to cure the SM.  It is
intended to reduce the pressure and stop the progression of the syrinxes.
Damage done to the brain and spinal cord before the surgery usually will not
be reversed, and most dogs will need to continue on medications afterwards,
including gabapentin or pregabalin and cortisteroids, depending upon the
severity of that damage before the surgeries.  The neurologists also
may recommend that the post-surgery patient undergo rehabilitation physical
therapy, in part to offset debilitating effects to the muscles, which may
result from long term doses of cortisteroids.
RETURN TO TOP
• Cranioplasty using titanium
The titanium procedure involves inserting titanium mesh to cover the
wider opening created by the FMD precedure.
(See image at right.)
In
a report published in July 2007
in Veterinary Surgery, Drs. Curtis W. Dewey and Dominic J. Marino wrote:
"Foramen Magnum
Decompression (FMD) with cranioplasty was well tolerated, with no
intraoperative complications, and minor postoperative complications. Most
dogs improved clinically, and none required further surgery at the original
FMD site."
Dr. Dewey also has reported that the "re-operation rate" has been
reduced to 10% or less of all FMD surgeries with the titanium mesh
cranioplasty. See more about Drs. Dewey and Marino under
Current
Research
below. Dr. Thomas
Schubert, formerly at the University of Florida, has applied a calcium-based
bone cement over the porous titanium mesh to further prevent scarring.
In
February 2022 article
, Italian neuro-surgeons reported on the use
of a customized 3-D-printed titanium prosthesis (device) as occipital
cranioplasty to cover the bone defect and enlarge the caudal fossa
(instead of the more traditional titanium mesh), following foramen
magnum decompression (FMD) in 8 CM/SM-affected dogs, including 6
cavaliers (75%). Each prosthesis was customized by
using computed tomography (CT) of the dog's skull, followed by 3-D
reconstruction of the skull to design the prosthesis.
(See photos of
one of the 3-D reconstructed skulls below.)
FMD was performed, and
the prosthesis was implanted in each case. Follow-up examinations were
performed 1, 6, and 12 months later, and the clinical status of each
dog's recovery was graded. Repeated MRI images of 5 of the cases were
compared to identify changes involving the neural
structures,
particularly the syrinx. The investigators reported that all prostheses
were easily positioned based on the pre-operative 3-D models, with no
complications. At 12 months after surgery, 3 cavaliers were free of
previous medications, and 2 CKCSs were still receiving steroid
medications but at lower doses. MRI of 4 cavaliers 6 to 20 months after
surgery revealed resolution of SM in CKCS Case 7, reduced size of SM in
CKCS Cases 2 and 4, and worse SM in CKCS Case 6. Details of each of the
6 cavalier cases
is reported here
RETURN TO TOP
• Cranioplasty using
LactoSorb SE mesh
LactoSorb SE mesh is a biodegradable polymer designed to
resorb in the human body by hydrolysis within a year.
Dr. Thomas
Schubert at the University of Florida has tried it instead of
titanium mesh in cranioplasty surgeries performed on cavaliers. He since has
switched back to using the titanium mesh. The polymer
reportedly is equal in strength to titanium at initial placement, retains
70% of its initial strength for the first eight weeks, and then gradually is
eliminated from the body.  It is manufactured by Biomet Microfixation,
LLC of Jacksonville, Florida.
RETURN TO TOP
• Duraplasty using
swine or bovine tissue
The alternative of a tent graft of swine or bovine collagen tissue and body
fat is called duraplasty.*
Dr. Andy Shores,
veterinary
It is called
duraplasty because the tissue is used as a substitute to the portion of the
dura which was cut during the surgery.
In a
report published in October 2009
at the American College of Veterinary
Surgeons' annual symposium, the researchers stated: "Overall, recovery
was considered to be good to excellent by owners. To date, none of the
patients that have undergone this surgical procedure have required further
surgical intervention due to postoperative compressive scar formation that
has been reported in the previous literature. Follow-up time ranges from 1
week to 1 year. ... The use of the titanium mesh, placement of the screws,
and the exothermic reaction of the overlying methyl methacrylate may
contribute to tissue trauma. The authors conclude that with the results of
this study, this procedure is clinically effective and the use of a titanium
mesh, additional hardware and methyl methacrylate offers no advantage in
canine COMS patients."
In a
March 2015 report
, Dr. Andy Shores and his surgical team at
Mississippi State University examined the results of 23 such duraplasty
surgeries they had performed, including 18 CKCSs. They noted that all of the dogs'
conditions had improved. Of 17 of the dogs, whose owners returned
surveys at least a year later, no dog has required additional surgery,
all but one had some improvement in quality of life after surgery, and
none were judged to deteriorate to less than the pre-surgical status. (
In
the MRI scan at right, taken a year after swine duraplasty surgery,
shows the location of the swine fat graft [FG]. Courtesy of Dr. Shores.)
In a
December 2017 article
, a team of Korean veterinary surgeons report
the successful grafting of Lyoplant, a pure collagen implant that is
produced from bovine pericardium, as a substitute for the portion of the
brain's dura removed during foramen magnum decompression surgery of a
Maltese dog diagnosed with Chiari-like malformation, and syringomyelia. They conclude
that "surgical decompression with Lyoplant was an effective long-term
(12-month) treatment for COMS without the need for any pharmacological
treatment."
RETURN TO TOP
• Duraplasty using
only patient's fat tissue
In a
2015 case study
, a team of Korean surgeons report the successful
duraplasty procedure on four CM/SM-affected dogs (breeds unidentified)
using only the patients' own fat tissue.
RETURN TO TOP
• Duraplasty using
tissue adhesives
Synthetic dural substitutes in duraplasty procedures
include inserting a soft foam consisting of a collagen-based matrix (e.g.,
DuraGen, by Integra LifeSciences Corporation). The collagen matrix supports
the ingrowth of local cells while the matrix itself is fully resorbed over
time.
Dr.
Michael Harrington, Animal Neurosurgery and Neurology, Murray,
Utah, reportedly uses this technique.
RETURN TO TOP
• Syringosubarachnoid shunt
The shunt consists of a small silicone tube. One end is
inserted into the subarchnoid space of the spinal cord below the syrinx, and
the other end is inserted into the syrinx (see below, left). Thus it is
called a syringosubarachnoid shunt (S-S shunt). Shunting drains the syrinx
fluid into the subarachnoid space where the usual CSF circulation and
absorption mechanisms exist. This should reduce the size of the syrinx and
ease pain and other the clinical signs associated with CM/SM.
"S-S shunting is a safe and relatively effective surgical technique that
may improve the neurological signs and the quality of life of dogs affected
by CM and associated SHM/SM. Postoperative complications or lack of clinical
improvement may occur in a small number of cases and a secondary surgery may
be needed. This study also suggests that the S-S shunt may lead to a
satisfactory outcome in dogs where the FMD [foramen magnum decompression]
technique has failed. Comparisons between different surgical techniques are
needed to create objective criteria that may suggest which procedure will
produce the best surgical results."
Mr. Skerritt and Dr. Motta may be contacted at ChesterGates
Animal Referral Hospital, Telford Court, ChesterGates, Chester, UK, CH1 6LT,
telephone 01244 853823, email GCSkerritt@aol.com.
In a
2018 article
, a team of Romanian veterinary neurosurgeons (Cătălina
Anca Cucoş, Ateş Barut, Iuliana Ionaşcu, Radu Constantinescu, Constantin
Vlăgioiu) report surgically inserting a shunt in a syrinx of a
4-year-old cavalier King Charles spaniel suffering from severe pain and
other signs due to Chiari-like malformation and syringomyelia (CM/SM).
The dog had undergone cranio-cervical decompression surgery a year
before before, which resolved the pain symptoms for three months,
followed by progressive deterioration afterwards. For the two months
prior to the shunt surgery, the dog's symptoms included neuropathic
pain, expressed by sudden yelping, neck and spinal discomfort,
scoliosis, apathy, depression, .phantom scratching and bunny-hopping
pelvic limb gait.
The
shunt was fashioned from a ventriculoperitoneal catheter
(right)
which was inserted into the syrinx to allow for drainage of
cerebrospinal fluid (CSF). The syrinx was located at C3-C4 and had a
maximum internal diameter of over 2 mm. The clinicians report that the
procedure was successful and that after three years, there remains
notably decreased neuropathic pain, with the intensity and frequency of
pain attacks reduced, scratching and yelping diminished, and overall, an
increased quality of life. They conclude:
"Syringosubarachnoid shunt placement represents a safe and efficient
procedure, which leads to clinical improvement of the clinical signs and
reestablishes the quality of life. Syringosubarachnoid shunting can be
an alternative option with good results, especially in cases in which
foramen magnum decompression has failed."
RETURN TO TOP
Ventriculoperitoneal shunt
"ventriculoperitoneal shunt" (VPS)
is a flexible
tube, called a catheter, one end of which is placed into one of the
lateral ventricles of the dog's brain, and the other end placed much
farther down the dog's body, to
drain
excess CSF away from the brain, where it can be absorbed by the body.
The purpose of shunting is to reduce pressure on the brain caused by the
excess CSF. If the dog has big ventricles (
ventricular
dilatation
) Dr. Rusbridge states that placing an
intraventricular shunt may be the best option.
A shunt
(right)
consists of three basic parts: (1) a
ventricular inflow catheter tubing, which drains the CSF from the
lateral ventricle; (2) a one-way pressure cutoff valve which regulates
the intracranial pressure by controlling the amount of fluid which flows
through the tubing; and (3) an outflow (distal) catheter at the other
end of the tubing, which is located lower in the dog's body, such as in
the abdomen, to be absorbed into the bloodstream and passed through the
urinary system. The catheters and tubing usually are made of radiopaque
silicone.
A computed tomography (CT) view showing
location of ventriculoperitoneal shunt placement, from its insertion
into the skull and down into the abdomen. Arrow points to the one-way
pressure cut-off valve.
VP shunts have become a standard method of treating
hydrocephalus
in dogs. At the 2023
meeting of the British Veterinary Neurology Society, Dr. Ana Fernandez
Cid reported on the successful insertion of a VPS for management of
CM/SM in a cavalier. The series of MRI images below, courtesy of
Dr. Rusbridge
, show in (a) the arrow pointing to the enlarged
ventricles, and in (b) a massive syrinx and developing pre-syrinx, prior
to VP shunt surgery.
In the post-operative MRI a month later, image
(c)
shows the two arrows pointing to the reduced size ventricles and the
shunt within them. In (d), the arrow points to the completely collapsed
syrinx and an almost normal spinal cord.
There are risks of compications and failure of VP shunts (e.g., see
this
April 2011 article
), including subdural hemorrhage.
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• Conclusion about surgeries
Dr. Rusbridge provides a detailed discussion of surgery on her
YouTube channel at this link
. She reports finding that:
• Surgery is an option particularly if the SM is progressive or
is poorly controlled by medication.
• Shunts aer most likely to
result in syrinx collapse but can be associated with serious
complications.
• Foramen magnum decompression (FMD) does not seen to
reverse the filling mechanism of the syrinx.
• FMD may result in
improvement of symptoms.
Many of these studies have been "case studies", meaning that they were
practiced without the controls normally included in clinical trials.
In the
July 2007 issue
of Veterinary Surgery,
Dr. Richard A. LeCouteur,
board certified veterinary neurologist at the University of California,
writes that:
"Medical history is replete with examples of invasive procedures
and pharmacologic interventions that were widely accepted based on results
of case studies, only to later be rejected based on results of controlled
clinical trials. ... It's time to adopt a more structured scientific
approach to the study of the management of neurologic conditions that may
benefit from surgical intervention. The randomized (preferably)
double-blinded (preferably) placebo-controlled study is the gold standard
for evaluating a new treatment intervention."
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Post-surgery soundwave therapy
Some cavalier King Charles spaniels, which have continued to suffer
severe pain due to post-decompression surgery scar tissue, have been
very successfully treated with an infrasonic instrument called AlphaSonic™.
This infrasound technology generates multiple, random, chaotic sound waves
in the range of Alpha (approximately 8 to 14 Hz), and unlike ultrasound
waves, does not heat body tissue.  Ultrasound uses a single high
frequency (from 20,000 to1,000,000 Hz) to stimulate a localized area and
heats tissue.
The manufacturer of the device represents that AlphaSonic™ is safer and
more effective than ultrasound, penetrates deeper into the tissues, reduces
inflammation, and softens scar tissue. It can be applied locally and at
acupressure points, and is said to increase blood circulation and can allow
the body to heal itself, much like the affects of acupuncture, but without
the needles.
The device is electrically operated and looks very similar to an
ultrasound unit.
Dr. Ronald J. Riegel
, DVM, who has studied
the effects of the AlphaSonic™ since 2001, stated, "The goal of any physical
therapy modality is to increase the circulation and increase the elasticity
and flexibility of the tissue. the alphasonic absolutely increases
circulation and allows the body to heal itself. The metabolism is increased,
reducing recovery times".
Adequate hydration is important for optimum bodily function. The dog
should be kept hydrated before, during, and after treatment with fresh clean
water. Although the manufacturer reports that AlphaSonic™ is totally safe
and that no negative side effects are known, any AlphaSonic™ treatments for
dogs with veterinary conditions, especially those taking medication, should
be performed only under the guidance of a qualified, licensed veterinarian.
For more information about AlphaSonic™, contact Susan Stoltz at AlphaSonic,
P.O. Box 2727, Valley Center, CA 92082, telephone 866-478-7118, email
info@thealphasonic.com
, website
www.thealphasonic.com.
RETURN TO TOP
Breeders' Responsibilities
SM is an inherited disorder that has a tendency to be more severe in each subsequent generation, and
with an earlier onset.  Breeders should follow the
SM Breeding Protocol
. Also, the confirmation
indicator research
described above
is
to aid in risk assessment to provide breeders with a tool to use with their
breeding stock.
RETURN TO TOP
What You Can Do
Send MRI scans
of cavaliers 5 years old or older and which do not have SM, along with MRIs
of those dogs' family members, to Dr. Clare Rusbridge at
c.rusbridge@surrey.ac.uk
When
lifting the dog, take care to support its entire body, including its
head and neck. See
this YouTube video
as an example of how to lift the dog.
Avoid
"triggers" which can prompt a CM and/or SM reaction in the dog. The main
trigger to avoid is walking the dog on a leash. Off leash exercise is
preferable.
Being
professionally groomed can be extremely distressing for CM/SM-affected
dogs, because the hands-on contact is constantly triggering.
Ease
your dog's symptoms by using a comfortable harness instead of a collar
attached to a
leash. The neck is one of the most vulnerable regions of the dog's
body. It houses the spinal cord,  vertebrae, muscles, the
tongue bone, the thyroid gland, the trachea, the esosphagus, major
blood vessels, lymph nodes, and the thymus. Pulling on the collar
can permanently damage any or all of these vital features.
One of the best harnesses for cavaliers with CM/SM symptoms
is the
BRILLIANT K9 "Lucy Small" harness
It is easy to put on and easy to take off. Watch the videos:
"Opening the harness"
and
"Walking the dog with the harness"
Provide affected dogs with raised food bowls so that they do not
have to use their necks to lower their heads to reach their meals.
RETURN TO TOP
Research News
RETURN TO TOP
Related Links
SM Breeding Protocol
Board Certified Veterinary Neurologists
MRI Screening Protocol
Ventriculomegaly
Estimated Breeding Values
Cerebellar Infarcts
Primary Secretory Otitis Media (PSOM)
Porencephaly
Questions for Cavalier Breeders
Canine Health Testing Clinics
Canine Chiari &
Syringomyelia Trust
Dr. Clare Rusbridge:
Dr.
Rusbridge's Comprehensive Website
Rusbridge/Knowler 2010 Research into CM Report
Dr. Rusbridge's Syringomyelia News Winter 2007 Research Update
Dr. Rusbridge's Syringomyelia News Autumn 2007 Research Update
Dr. Rusbridge's Syringomyelia News 2007 Research Update
Dr. Clare Rusbridge video DVD "Syringomyelia Seminar", contact
penny.knowler@ntlworld.com
The Canine Chiari Institute
A website devoted to syringomyelia in Cavaliers is Karlin Lillington's
SM.CavalierTalk.com
Margaret Carter's
"About SM"
webpage
Two SM support email groups for owners of dogs with SM are
Yahoo! Group:
Arnold Chiari Dogs
and
Yahoo! Group:
CKCS SM-support
Two SM email discussion groups are
Yahoo! Group: CKCS-SM
and Karlin Lillington's
CavalierTalk: SM
and MVD Cavaliers Forum
A website and a book about a Cavalier diagnosed with syringomyelia is
at
For the love of Ollie
UK Cavalier Club's List of MRI Scanned USA Cavalier Breeding Stock
Cavalier Owners' Blogs:
Rosie's Life With Syringomyelia
Our Journey with Toby
& Syringomyelia
All about Minnie
(Moo)
Ella's
Battle With Syringomyelia
Riley's Beating
Syringomyelia
Abbey our
CKCS and her family's Syringomyelia Journey
Lucy Magic Sky
Brussels Griffon Owner's Blog:
Friends of Lola
Webpages from Laura Lang's
CKCS Info Center website
showing additional MRIs
and x-rays of SM-affected or CM Cavaliers:
MRI image primer
MRI
images of Cavaliers diagnosed with and without the malformation and SM
For answers to frequently asked questions about MRIs and what to expect if
your dog is to undergo one, see
PetsDx - Pet Owners Frequently Asked Questions
YouTube videos of cavaliers with SM
RETURN TO TOP
CM and
SM in Other Breeds
Other breeds known to be affected by Chiari-like malformation and
syringomyelia include the
Affenpinscher
,  Bichon Frise,
Boston terrier
Brussels Griffon (Griffon Bruxellois)
, bull terrier,
Chihuahua
, French
bulldog,
Havanese, King Charles spaniel (the English toy spaniel),
Maltese
terrier
, miniature dachshund, miniature and toy poodles,
Papillon,
Pomeranian
Pug, Shih Tzu,
Staffordshire bull terrier, and the Yorkshire
terrier, as well as cross-breed dogs, particularly CKCS crosses.  Up to
65% of MRI'd Griffon Bruxellois breed have been found to have CM. In a
September 2017 article
, 100% of 53 Chihuahuas had CM and 38% of them had
SM. Click on the breeds' hyperlinked names to link to Internet articles
about CM and SM in those breeds. In a
December 2023 article
, a study of 3,796 Pomeranians, 25% of them were
diagnosed with SM.
In this
October 2024 article
, Dr. Paul Mandigers and fellow
researchers studied MRIs of several small breeds, including the
chihuahua, daschshund, French bulldog, Maltese, miniature schnauzer,
Pekinese, pug, Shi Tzu, Yorkshire terrier, and a few un-named "various
breeds/crosses". They report finding:
"There was no statistically significant difference for breed and sex
(p = 0.32) or breed and age (p = 0.318), meaning that sex and age were
comparable for all breeds. However, there was a statistically
significant difference for all breeds for CM (p < 0.001), SM (p = 0.003)
and syrinx size (p = 0.003), meaning that CM1/CM2 and SM+ were present
at a significantly higher rate in all breeds. CM was seen the most in
the Chihuahua (75%), Griffon (96%), Maltese (83%), Pug (75%) and
Yorkshire terrier (80%) breeds. CM and/or SM were only seen in one out
of nine Dachshunds. SM was observed in all breeds, with the highest
frequency in the Griffon (89%), French Bulldog (70%) and Chihuahua
(62%). Only in the French Bulldog was there evidence of a high number of
dogs being affected by SM and not CM. In all other breeds, CM and SM
appeared to predominantly occur simultaneously. In all breeds, SM was observed with an average syrinx size of
2.9 ± 2.4 mm (Mean ± SD), with the French Bulldog, Pug, Griffon and
Chihuahua having larger syrinxes. MEE was only seen in the French Bulldog, two Chihuahuas and four
crosses.
* * *
"In this group of small dog breeds, scanned
because of the presence of neurological signs, CM and SM occurred in all
breeds. It must be stressed that this is not a randomly chosen group of
dogs, and all dogs included were scanned for a diagnostic reason. ...
But in this group of small dogs, CM and SM was seen in all breeds. For
the brachycephalic breeds, this was expected. There is an association of
CM and brachycephaly. The findings in the four typical brachycephalic
breeds, the French bulldog, Chihuahua, Griffon, and Pug, are therefore
not surprising. The presence of CM and SM in both the Chihuahua and
Griffon has also been reported earlier. Reports on CM/SM in the French
Bulldog or Pug are anecdotal. In 2012, the French Bulldog was actually
used as a control group for a CKCS study but based on our findings, the
French Bulldog is not a suitable control group for the CKCS. It appears
to be one of the breeds with a high incidence of SM. And although the
number of Pugs in this study was small, CM and/or SM appears to occur
with similar frequencies as within the French bulldog."
RETURN TO TOP
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Blood Pressure
Brachycephalic
Brachycephaly
Breathing
Cancer
Canine Atopic Dermatitis
Cannabidiol (CBD)
Cannabis
Cardiac Valve Disease (CVD)
Cardiologists
Cataracts
Cavalier Club
Cerebellar Infarct
Cervical Spondylomyelopathy
Cherry Eye
CHF
Chiari-like Malformation
(CM)
Chondrodystrophy (CDDY)
Chronic Enteropathy
Chronic Pancreatitis
Chronic Ulcerative Paradental
Stomatitis (CUPS)
CM/SM
Coconut Oil
Cognitive Dysfunction
Colitis
Congestive Heart Failure (CHF)
Conjunctivitis
Copper
Associated Hepatitis
Corneal Dystrophy
Corneal Melting
Corneal Ulcer
Crossbreeding
CUPS
Curly Coat Syndrome
Cushings Disease
DCM
Deafness
Degenerative Myelopathy
(CDM) (DM)
Dental Disorders
Dermatitis
Dewclaws
Diabetes Mellitus
Diarrhea (Diarrhoea)
Diets
Dilated Cardiomyopathy
(DCM)
Disc Disease
Distichiasis
DM
DNA
Dry Eye Syndrome
Elbow Disorders
Elongated Soft Palate
Encephalitis
Endocardiosis
Enteropathy
Entropion
Eosinophilic Stomatitis
EPI
Epiglottic Retroversion
Epilepsy
Episodic Falling Syndrome
Estimated Breeding Values
Everted Laryngeal Saccules
Exocrine Pancreatic Insufficiency (EPI)
Eye Disorders
Facial
Nerve Paralysis
Fear Avoidance
Femoral Artery Occlusion
Follicular Cystitis
Fly Catchers Syndrome
Food
Gallbladder Disorders
Gastroenteritis
Gastroeosophageal reflux disease (GERD)
Gastrointestinal
Genetics
Genetic Tests
Gestation
Gingivitis
Glaucoma
Glue Ear
Growth Plate
Gum Disorders
HD
Hearing
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Heartworm
Heatstroke
Hemorrhagic Gastroenteritis (HGE)
Hepatic Disorders
Hernia
Hip Dysplasia (HD)
Horner Syndrome
Hydrocephalus
Hydromyelia
Hydrosyringomyelia
Hyperadrenocorticism
Hypercortisolism
Hypersialism
Hypoadrenocorticism
Hypothyroidism
IBD
Immune-Mediated Polyarthritis
(IMPA)
Infarcts
Inflammatory Bowel Disease (IBD)
Insecticide Poisoning
Intervertebral Disc
(IVDD)
KCS
Keratitis
Keratitis Sicca
Keratoconjunctivitis Sicca (KCS)
Keratomalacia
Kidney Disease
Knee Dislocation
Laryngeal Collapse
Liver Disorders
Liver Shunt
Lock Jaw
Lung Collapse
Lungworm
Macrothrombocytosis
Mange
Masticatory Muscle Myositis
MCAD Deficiency
MCT Oils
Megaesophagus
Meningoencephalitis
Microphthalmia
Middle Ear Effusion
Miscellaneous Disorders
Mitral Valve Disease
MRI Screening of SM
Muscle Hypertonicity
Muscular Dystrophy (MD)
MVD
MVD Breeding Protocol
Myoclonus
Neurologists
Neutering
Obesity
Orofacial
Clefts
Osteoarthritis
Outcrossing
Overview
Pacemaker
Palmitoylethanolamide
Pancreas
Pancreatitis
Panting
Parasites
Patellar Luxation
Patent Ductus Arteriosus (PDA
PDA
PEA
Periodontal Disease
Periodontitis
Piebaldism
Plants
-- toxic, poisonous
Platelets
Pneumocystis Pneumonia
Pneumothorax
Polyarthritis (IMPA)
Porencephaly
Portosystemic Shunt
Pregnancy
Presyncope
Primary Secretory Otitis Media
Progressive Hereditary Deafness
Progressive Retinal Degeneration (PRD)
Progressive Retinal Atrophy
(PRA)
Protein-Losing Enteropathy
PSOM
Pulmonary Hypertension
Pulmonary Thrombosis
Pulmonic Stenosis
Pyometra
Pyrethrins
Raw Food & Diets
Renal Disease
Rescue
Retinal Atrophy
Retinal Degeneration
Retinal Dysplasia
Reverse Sneeze
Rough Coat Syndrome
Salivary Glands
Sand Impaction
Sedation
Shadow Chasing
Skin Conditions
Sleep Disorders
SM
SM Breeding Protocol
SM MRI Screening
Snoring
Spaying
Stenotic Nares
Stroke
Syncope
Syringomyelia
Syringohydromyelia (SHM)
Syrinx
Teeth
Teeth
Chattering
Temporomandibular Joint
Morphology
Thrombocytopenia
Thyroid Disorders
Thyroiditis
Trachea
Tracheal
Collapse
Ulcerative Stomatitis
Urinary Tract
Uroliths
Vasculitis
Ventriculomegaly
Vestibular Syndrome
Vision Disorders
Wobbler Syndrome
Xanthinuria
Zinc Toxicity
Zoonotic Diseases
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