Syringomyelia (SM) and the
Cavalier King Charles Spaniel
- IN SHORT
- IN DEPTH
- CM - OH - COMS
- CHIARI-LIKE MALFORMATION
- - CM research history
- -CM recent findings
- - pain due to CM
- WHAT SM IS
- - MRIs
- - CTs
- - thermography
- - ultrasound
- - BAER
- - physical exam
- MRI CLINICS
- DNA TESTING
- - drugs
- - alternative care
- - surgery
- - soundwave therapy
- BREEDERS' RESPONSIBILITIES
- WHAT YOU CAN DO
- RESEARCH NEWS
- RELATED LINKS
- CM & SM IN OTHER BREEDS
- VETERINARY RESOURCES
- PAGE 2 of SYRINGOMYELIA
- PAGE 3 of SYRINGOMYELIA
Syringomyelia (SM) is an extremely serious condition in which fluid-filled cavities 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.
The back half of the cavalier King Charles spaniel’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 – partially blocking the flow of cerebrospinal fluid (CSF) down the spinal cord. The variable pressure created by the abnormal flow of CSF is believed to create the SM cavities – called syrinx – in the spinal cord.
SM is rare in most breeds but has become very widespread in cavalier King Charles spaniels and the Brussels Griffon (Griffon Bruxellois). The number of diagnosed cases in cavaliers has increased dramatically since 2000. Researchers estimate that up to 95% of CKCSs may have Chiari-like malformation (CM or CLM) – also known as caudal occipital malformation syndrome (COMS) or occipital hypoplasia (OH), the skull bone malformation present in all cases and believed to be at least part of the cause of syringomyelia – and that more than 50% of cavaliers 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 ...
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.
Pain is the most important clinical sign of the disorder. 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 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 ...
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.
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. More ...
Treatment options for SM are very limited. 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.
Anticonvulsants, such as gabapentin (Neurontin, Gabarone), have been successful in some more severe cases, but they may be very expensive. Pregabalin (Lyrica), 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.
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 ...
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.
What You Can Do
• Donate to the Cavalier Health Fund.
• Donate by buying the book, For the love of Ollie.
• Participate in the Syringomyelia Cavalier Collection Scheme.
• Ease your dog's 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".
Syringomyelia (SM -- also known as syrinx and hydromyelia, and occasionally mis-identified as Arnold Chiari malformation) is a condition of the development of fluid-filled cavities in the spinal cord, which is believed by researchers to be due to abnormal flow of cerebrospinal fluid (CSF) between the brain and the spinal cord through the foramen magnum at the base of the skull.
SM was first identified by veterinary neurologists in the late 1990s, while classic symptoms, such as air scratching, had been reported anecdotally prior to then.
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 syringo-hydromyelia (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 Chiari-like malformation (CM or CLM). 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.
SM is rare in most breeds but reportedly has become very widespread in cavalier King Charles spaniels and the Brussels Griffon (Griffon Bruxellois). 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 believed to be 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.
*A 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.
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 Frisé, Boston terrier, bull terrier, Chihuahua, 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.
Chiari-like malformation (CM or CLM) -- Occipital hypoplasia (OH) -- Caudal occipital malformation syndrome (COMS)
These three terms 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.
*Cavaliers have been determined to be brachycephalic. See 2011 report.
Chiari-like malformation (CM or CLM) is named after a similar condition in humans, discovered by Dr. Hans Chiari. Chiari-like malformation is 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." The foramen magnum is a hole in the back of the skull -- the occipital bone -- which leads to 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.
* The definition of this term underwent a revision in 2010. 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."
In an October 2014 article, UK researchers found three different definitions of 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."
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."
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. Therefore, other factors are believed to 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.
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 Chiari-like 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."
"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 the premature closure of the skull's growth plate.
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."
In a 2010 UK study report in the Journal of Small Animal Practice (JSAP), Colin J. Driver (right), Dr. Clare Rusbridge, et al. reiterated findings that the variations in the dimensions of the cavaliers' posterior [caudal] cranial fossa* may not be associated with syringomyelia, since cavaliers do not have a proportionately smaller caudal cranial fossa compared to other small breeds. See, also, an abstract of that study presented before the European College of Veterinary Neurology (ECVN).
*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."
--- most recent findings of Chiari-like malformation research
In an April 2012 study by Thomas A. Shaw, Imelda M. McGonnell, Colin J. Driver, Clare Rusbridge, and Holger A. Volk, they concluded that:
"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 signalling 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."
"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.
In an April 2015 article by Drs. S. Cerda-Gonzalez, N.J. Olby, E.H. Griffith, on the subject of the kinking (or elevation) of the medulla, they examined 36 cavaliers (33 having Chiari-like 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". )
--- 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. 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.
-- 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, Drs. Sofia Cerda-Gonzalez, Natasha J. Olby (left), Susan McCullough, Anthony P. Pease, Richard Broadstone, and Jason A. Osborne 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 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."
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.
-- caudal occipital malformation syndrome (COMS)
Caudal occipital malformation syndrome (COMS) had been used, particularly by some specialists in the United States, to describe the disorder. However, at the November 2006 London conference, the term COMS also was rejected because there is no proof yet that the condition is related to a malformed occipital bone. Nevertheless, some diehard neurologists in the northeast USA persist in using this term when referring to Chiari-like malformation in cavaliers. Similarly, 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."
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. See Karen Kennedy's* Understanding Canine Chiari Malformation and Syrningomyelia for scans of the occipital bone and foramen magnum, comparing "normal", mild Chiari" and "severe Chiari" dogs.
* 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.
Dogs with CM but not syringomyelia (SM) can experience discomfort, including pain. This is attributed to a direct compression of the medulla oblongata, which is involved in the modulation of pain. See our section on expressions of pain as a symptom of SM, below, for information about CM and SM pain research.
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.
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).
Cerebrospinal fluid 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. 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. (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.)
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.
-- role of the ventricle system (vetricular 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. In a December 2010 UK study, also 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.
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.
-- 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.
Symptoms may vary widely among different dogs, but the earliest sign 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 (phantom scratching). This is 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), which prompt the dog to scratch. Some dogs perform facial or head rubbing or spontaneous vocalizations. Click here or the YouTube logo (below right) to see videos of cavaliers with SM symptoms.
Many symptoms of CM and/or 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 9-month old cavalier at left with scoliosis.* An outward deviation of an eye, called exotropia also is common among dogs affected with CM.
*Photo is from Dr. Clare Rusbridge.
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.
The condition 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 Chiari-like malformation (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.
An excellent review of the various symptoms displayed by dogs affected with syringomyelia may be found on the SM.CavalierTalk.com website, prepared by Karlin Lillington of Dublin, Ireland. Her website includes videos of SM-affected dogs. Other videos are available under Related Links below.
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".
As the disorder progresses, there usually follows increasingly severe pain around the dog's head, neck, and shoulders, causing it yelp or scream.* It is believed to be a neuropathic pain, probably due to disordered neural processing in the damaged dorsal horn.
Nevertheless, as recently as October 2012, researchers still state that, "It is not yet fully understood how CM/SM causes NeP [neuropathic pain]."
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.
As the disease 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.
*Photo at right above is of a cavalier suffering severe head pain due to SM. Photo below left is of a cavalier writhing in pain from SM. Photo above is from Dr. Clare Rusbridge. Photo below is from Pedigree Dogs Exposed.
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."
Syringomyelia can be very deceptive because some symptoms (which may include paw licking, head shaking, head rubbing, circular walking, fly biting, and reluctance to defecate) are common behaviors for many unaffected dogs. One distinction is that dogs suffering from SM engage in these patterns excessively and seemingly compulsively. So, other causes of the dog's symptoms need to be considered and should be ruled out before concluding that SM is the cause. For example, if a syrinx develops in a lower area of the spine, such as the lumbar region, the dog may scoot excessively, even to the extent of rubbing the anal area raw. However, scooting is a common symptom of other disorders, or even of no particular disorder at all.
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 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 (Lynda Rutherford, Annette Wessmann, Clare Rusbridge, Imelda M. McGonnell, Siobhan Abeyesinghe, Charlotte Burn, and Holger A. Volk) 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 Hilary Zhaoxu Hu, Clare Rusbridge, Fernando Constantino-Casas, and Nick Jeffery 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 M.J. Schmidt, J. Roth, N. Ondreka, M. Kramer, and C. Rummel 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 asymmetrical syrinxes or involvement of the dorsal horn gray matter. They also found that cavaliers with clinical signs of pain showed a presence of interleukin-6 (a key component of the nervous system’s response to injury) and substance P (a neurokinin that regulates the immune functions of spinal glial cells) in their cerebrospinal fluid (CSF). 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. (In the study's photo above, the top three syrinxes are asymmetrical; the bottom three are symmetrical.)
In a May 2014 report, USA Drs. S. Cerda-Gonzalez, N.J. Olby, E.H. Griffith 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 matter 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."
-- other disorders with similar symptoms
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.
Also, see flycatcher's syndrome for a description of another disorder prevalent in CKCSs and which has identical symptoms to the fly biting of some SM/CM-affected dogs.
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.
Dr. Rusbridge has a website, veterinary-neurologist.co.uk, which discusses SM extensively, as well as other neurological disorders which she has researched. Her doctoral thesis, a 200+ page book (right), Chiari-like Malformation and Syringomyelia in the Cavalier King Charles Spaniel, also is available online, for free.
-- magnetic resonance imaging (MRI)
The only accurate way of diagnosing the disease is said to be through the use of magnetic resonance imaging (MRI) scanning. 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 examiing 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.
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.
The MRI scan of a cavalier 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 study conducted by Dr. Rusbridge and Ms. 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.
-- computed tomography (CT)
Computed tomography (CT) is an imaging method using digital geometry processing to generate a three-dimensional image of the inside of an object from a large series of two-dimensional x-ray images taken around a single axis of rotation. Researchers have been studying the value of CT scans to detect Chiari-like malformations and syrinxes in cavaliers and comparing the results with MRIs and other resources. In a very preliminary 2008 French study, researchers CT scanned sixteen CKCS to measure the size of their caudal fossas and to determine standard computed tomography dimensions of the caudal fossa.
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."
However, since both of these Belgian studies were limited to detecting Chiari-like malformation, there remains the question of the comparative value of CT-scanning for diagnosing syrinxes.
-- thermography (medical infrared imaging -- MII)
Medical infrared imaging (MII), also called thermography, is a non-invasive imaging technique which records thermal patterns. It provides information about the function of the sympathetic nervous system. Thermal imaging has drawn the interest of veterinary researchers as a potential screening test for CM in dogs due to its ability to image dogs without sedation. In a preliminary 2007 study at Long Island Veterinary Specialists (LIVS), Dr. Dominic J. Marino's team found that cavaliers with CM had “cooler” thermographic patterns when compared with a dog with a normal caudal fossa. Dr. Marino reported in October 2007 that, "based on these very preliminary findings, thermography may be a viable imaging modality to use as a screening tool to detect CLM in dogs."
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."
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.email@example.com, telephone 0844 544 3314, website www.veterinary-thermal-imaging.com
In 2005, Drs. Dominik Faissler and John (Jay) McDonnell, board certified veterinary neurologists at the Cummings School of Veterinary Medicine at Tufts University in Massachusetts, researched the use of ultrasonography to diagnose syringohydromyelia in dogs. In a 2005 interim report, they stated, "This preliminary study indicates that cervical spinal cord ultrasound can be useful as a diagnostic aid for CM. It cannot rule out a diagnosis of CM, however no false positives were found. To investigate the sensitivity and specificity of this imaging modality blinded U/S examination of large numbers of dogs after MRI evaluation is planned."
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."
-- brainstem auditory evoked response (BAER)
A supplemental diagnostic screening tool used by at least two veterinary neurologists, Dr. Curtis W. Dewey and Dr. Georgina Barone, and by Dr. Dominic J. Marino is the BAER (for Brainstem Auditory Evoked Response) test. The BAER test measures the timing of electrical waves from the brainstem in response to clicks in the ear. Dr. Dewey reported that, assuming the dog is not deaf, the detected brain waves can be used to assess the integrity of the brain stem, since CM involves some degree of brain stem compression.
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."
In a 2014 study of 133 cavaliers, researchers (Thomas J. Mitchell, Susan P. Knowler, and Clare Rusbridge, and consultants in the Netherlands and Canada, Henny van den Berg and Jane Sykes) 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.
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 to manage the suspected CM/SM. 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.
The following MRI photographs, and their descriptive text, are courtesy of Dr. Clare Rusbridge and Ms. Penny Knowler of Stone Lion Veterinary Centre:
Left: This image shows mild Chiari-like malformation – the cerebellum is very slightly indented, the kinking of the medulla is normal for a toy breed and there is displacement of the cerebellum into and just out of the foramen magnum. The ventricular system is slightly dilated.
Right: Although the cerebellum is not coming through the foramen magnum, this dog has a greater degree of Chiari-like malformation than the first dog. The cerebellum is indented, and the medulla is kinked. The central canal is dilated above the first disc space – this is the first sign of syringomyelia developing. There is also mild ventricular dilatation.
Left: This dog has descent of the cerebellum towards the foramen magnum and the cerebellum is indented. The medulla is normal for a toy breed; there is mild ventricular dilatation and a small syrinx/central canal dilatation in the upper cervical spinal cord.
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.
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.)
Dr. Jill Narak,
board certified veterinary neurologist, is offering MRI scans for $750.00,
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. Narak (Email: firstname.lastname@example.org) or Dr. John Hathcock (Email: email@example.com) 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 $750.00, which include the 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"). Recent blood work (no older than one month) is required or can be performed at the hospital. Contact Dr. Sammut at VCA-West Los Angeles, at 1818 S. Sepulveda Blvd., Los Angeles, CA, 90025, Tel: 310-473-2951, Email: firstname.lastname@example.org, website: www.vcawla.com
REDWOOD CITY, CA: AnimalScan at 410 Brewster Avenue, Redwood City, CA 94063, telephone 650-480-2001, email email@example.com See Easton, PA entry for details.
WEST HARTFORD, CT: Companion MRI, located at 993 North Main St., West Hartford, CT 06117. They offer a mini-MRI scan for $750.00 and a full-MRI scan for $1,250.00, which includes a pre-anesthesia exam, anesthesia and monitoring during the MRI scan, a "high-field" MRI scan, MRI interpretation by a board certified radiologist, and a CD of the scan images. They offer reduced fees for groups of dogs. A veterinarian must refer the patient for these scans. Some financial assistance is available. Contact Alycia Pronesti, telephone 860-586-8610, E-mail: firstname.lastname@example.org, Website: companionmri.com
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 email@example.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 the University of Iowa 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 Veterinary Specialty Center (VSC), an affiliate of MSU, 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 (serum chemistries, electrolytes, CBC, urinalysis) or these tests can be performed on-site (cost: up to $35.00). A complete physical and neurologic examination will be provided at no additional cost. A metal Screening CT scan – required before all MRI exams will be performed for $55.00. Sedation/anesthesia, including an IV catheter and full and constant monitoring will be provided for $100.00. An MRI screening (3T magnet: Sagittal T2, Transverse T1 and T2) will be performed at a cost of $445.00. This also also screens for primary secretory otitis media (PSOM). The approximate total cost for a single patient is $600.00; however, if VSC screens 3 patients in one day, the cost will be approximately $550.00 each. The multiple patients screening is designed to accommodate owners with several dogs being considered as part of a breeding program. For the pricing break, VSC 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 $500.00, 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 firstname.lastname@example.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 email@example.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 firstname.lastname@example.org
MONTREAL, QC: Hospital Veterinaire de l’Est, 8700, av Chaumont, Montreal (Anjou), QC H1K 1N6 offers MRI scans for $500.00 CDN (blood work not included). Scans are sent to Oregon to be reviewed and graded. Telephone 514-3558322, website www.monvet.com The CKCS Canada Club contact is Tessa Robillard, email@example.com
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, firstname.lastname@example.org , 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 $525.00 ($500.00 for 3 dogs of same owner). The clinic has three independent board certified veterinary radiologists available to read and report the results, within 24 hours. The price includes: IV cathater, anesthesia (typically Propofol induction and inhalant isoflourane), IV contrast, neuro-cranium MRI (multiple views to include sagittal, transverse, dorsal weighted at T1/ T2, etc.), scan review and report by the radiologist, 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 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 email@example.com or Blueridgevets@aol.com, website www.PetMRimaging.com
TACOMA, WA: Puget Sound Veterinary Referral Center, 5608 South Durango St, Tacoma, WA 98409, offers an MRI scan, including a CD of images and a written report, for $850.00 (blood work included). Contact them at 253-474-0791, website www.theaec.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
Dr. Rusbridge reported in May 2010 that genetic researchers Quoc-Huy Trinh, Penny Knowler, Alexandra Thibault, Marie-Pierre Dubé, Guy A. Rouleau, Clare Rusbridge, and Zoha Kibar may have found the site for SM on the cavalier's genome. In a May 20, 2010 update on her website, Dr. Rusbridge publishes an interim report in highly technical wording, which states that they have located a haplotype which contains mutations in SM-affected dogs and does not contain such mutations in unaffected cavaliers. Gene sequencing and additional mapping of the locus are under way.
A team of Montreal researchers, including LeMay P, Trinh QH, Dubé MP, Rusbridge C, Rouleau GA, and Kibar Z, reported in June 2011 that they had identified a chromosome 2 region associated with Chiari-like malformation in the Brussels Griffon breed. See summary here.
In April 2014, the research team of Philippe Lemay, Susan P. Knowler, Samir Bouasker, Yohann Nédélec, Simon Platt, Courtenay Freeman, Georgina Child, Luis B. Barreiro, Guy A. Rouleau, Clare Rusbridge, and Zoha Kibar reported finding in the Brussels Griffon a potential "candidate" gene, SALL-1 in the Canis Familiaris Autosomes (CFAs) region CFA2 quantitative trait locus (QTL) . In other mammals, SALL-1 is known to be important in the development of the hind brain. They also identified CFA14 as another possible locus of a gene involved in the development of CM. As of 2014, similar research is underway with CKCSs.
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.
* Chiari-like malformation (CM) also has been found to be progressive in some cavaliers.
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."
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 diagram of treatment options, which she calls a treatment algorithm, which is downloadable here in pdf format.
. 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."
Treatment options for CM/SM are very limited. However, some medications have been effective in some cases. The two photos to the right 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, such as gabapentin (Neurontin, Gabarone), have been successful in relieving neuropathic pain, which is evidenced by behaviors such as sensitivity to touch or phantom scratching. Gabapentin 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. 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.
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. 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.
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.
A newer anticonvulsant, pregabalin (Lyrica), is being prescribed by some neurologists in treating SM. It is closely related to gabapentin and was developed by Pfizer, which also developed gabapentin. Pfizer reports that pregabalin is more potent than gabapentin and achieves its effect at lower doses. Doses of pregabalin also reportedly have a longer lasting effect than gabapentin. No generic version is available, and as an exclusive brand, Lyrica is quite expensive in comparison to generic gabapentin.
Amitriptyline (Elavil, Tryptizol, Laroxyl, Sarotex) is a tricyclic antidepressant (TCA) by Merck which may be prescribed as an alternative to either gabapentin or pregabalin.
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. Methylsulfonyl-methane (MSM) is recommended by some veterinary neurologists as a dietary supplement.
--- NSAIDs, for non-neuropathic pain from Chiari-like malformation
The use of non-steroidal anti-inflammatory drugs (NSAIDs), such as carprofen* (Rimadyl, Quellin), meloxicam (Metacam), firocoxib (Previcox), mavacoxib (Trocoxil), and aspirin, may relieve the symptoms of non-neuropathic pain, such as is caused by the Chiari-like malformation rather than from the syringomyelia, as evidenced by yelping when either being picked up of changing posture. These drugs do not retard deterioration due to progression of the SM.
*Carprofen (Rimadyl, Quellin) may have serious side effects and should not be given without a veterinarian's close guidance and monitoring.
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.
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."
--- 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.
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.
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.
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.
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.
Another H2-blocker occasionally prescribed is Pepcid AC (famotidine).
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. Diuretics are being used infrequently, due to side effects and the success of other CSF pressure reducers.
--- 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. 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.
--- other drugs
Some neurologists are prescribing amantadine (Endantadine, Symmetrel), 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.
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.
Before the disease progresses to its severe form, the use of anti-inflammatory corticosteroids, such as prednisolone (Prelone), methyl-prednisolone (Medrol, Medrone), and dexamethasone (Decadron, Dexamethasone Intensol, Dexone, Hexadrol), may relieve the symptoms but not the deterioration. However, dogs should never be treated with both a cortisteroid and an NSAID at the same time. See this March 2011 report.
Corticosteroids 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.
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).
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.
Some owners of SM dogs report that periodic treatments of acupuncture (above right) provide relief.
Surgery to allow the cerebrospinal fluid to flow normally may be necessary to reduce the pain and deterioration. Surgery is recommended if there is significant pain or a deteriorating condition. It usually is successful in significantly reducing the pain and improving the neurological deficits. Neurologists experienced with CM and SM in cavaliers 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.
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.
One form of surgery is called foramen magnum decompression (FMD), or suboccipital 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. A less frequent surgical procedure is subarachnoid shunting, which essentially is a salvage operation when the surgeon has no other surgical options. All FMD surgeries are technically difficult and should be performed only by experienced neurological surgeons.
Although this form of surgery often is successful, it may be expensive, and many dogs may either have a recurrence of the disease or still show signs of pain and 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. 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), or covering the sutured dura with a tented graft of swine intestine tissue, covered by a layer of the dog's fat tissue.
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.
--- cranioplasty using titanium
The titanium procedure is called cranioplasty. Dr. Curtis W. Dewey, veterinary neurologist in New York, and Dr. Dominic J. Marino, board certified veterinary neuro-surgeon, also in New York, and Dr. Wayne L. Berry, veterinary neurologist in California inserting the titanium mesh in several surgeries thus far. And now other specialists, including Dr. Graham Oliver in the UK, are performing the cranioplasty procedure.
In a report published in July 2007 in Veterinary Surgery, Drs. Dewey and 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 at the University of Florida applies a calcium-based bone cement over the porous titanium mesh to further prevent scarring.
--- 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.
--- duraplasty using swine tissue
The alternative of a tent graft of swine tissue and body fat is called duraplasty.* Dr. Andy Shores, veterinary neurologist at Mississippi State University (previously at Auburn in Alabama), Dr. Jill Narak, veterinary surgeon at the University of Tennessee in Knoxville, and others have performed this procedure on at least 21 dogs, most all of them cavaliers. Swine intestinal submucosa was sutured over the cerebellum and brain stem in a tented fashion (see photo). Fat tissue from the dog's gluteal region was then placed over the site prior to routine closure.
* 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."
--- 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.
--- syringosubarachnoid shunt
Another form of surgery, performed by veterinary neurosurgeon Geoffrey Skerritt, BVSc, MIBiol ,CBiol, DipECVN, FRCVS (at right), in the United Kingdom, and others, involves inserting a shunt, rather than removing the supraoccipital bone or a portion of the atlas. He is said to prefer the shunt because it reduces the higher risk of nerve damage and blood loss in decompression surgery, and it lessens the possibility of the cerebellum continuing to herniate.
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.
In an April 2012 study of S-S surgeries conducted on nine cavaliers and two Yorkshire terriers, Geoff Skerritt and Dr. Luca Motta reported that:
"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.
--- conclusion about surgeries
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."
-- 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 760-751-2836, email firstname.lastname@example.org, websites www.alphasonic.com and www.makepaingoaway.com
SM 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.
• Donate to the Cavalier Health Fund.
• Donate by buying the book, For the love of Ollie.
• Participate in the Syringomyelia Cavalier Collection Scheme.
• Ease your dog's 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".
Finningley, Doncaster, UK -- February 1, 2015 -- Northern and Eastern Counties Papillon Club. "Syringomylelia and Chari-like Malformation", featuring Penny Knowler. The seminar will be held at Finningley Village Hall, Finningley, Doncaster, DN9 3DA. The cost of £15-00 includes lunch. The club also will be holding a raffle and donating part of the entry fee to the research programe. Contact Eileen Roberts at 0116 2570277 for reservations or additional information.
Chieveley, UK -- November 17, 2013 -- South of England Pomeranian Club. "Canine Chiari-like malformation, Syringomyelia (CM/SM) & Canine Epilepsy" featuring Dr. Clare Rusbridge. Details here.
International Symposium on Syringomyelia held October 23, 24, 25, 2007 in Rugby UK, sponsored by The Ann Conroy Trust, with the University of Birmingham, the Society of British Neurological Surgeons, and the Spine Society of Europe. Speakers were Clare Rusbridge, Dominic Marino, Graham Flint, Guy Rouleau, and Sarah Blott. Obtain compact discs of all five talks and the hour long Q&A session with leading experts on syringomyelia and the Chiari-like malformation in cavaliers, for a contribution to support CKCS genome research at http://www.cafepress.com/cavaliertalk/4311456
Syringomyelia International Conference held November 11, 2006 at the Royal Veterinary College: Read summaries of presentations by Clare Rusbridge, Paul Mandigers, Laurent Cauzinille, Harvey Carruthers, Nick D. Jeffery, Catherine A. Loughin, Martin Deutschland, Dominic J. Marino, and G. Flint, and view their slide presentations.
CM and SM in Other Breeds
Other breeds known to be affected by Chiari-like malformation and syringomyelia include the Affenpinscher, Bichon Frisé, 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 Chiari-like malformation. Click on the breeds' hyperlinked names to link to Internet articles about CM and SM in those breeds.