Canine Chiari-like Malformation & Syringomyelia (CM/SM)
I am grateful to Dr Clare Rusbridge BVMS PhD DECVN MRCVS, who has given me permission to re-print her paper on Canine Chiari-like Malformation and Syringomyelia (CMSM) (November 2008). Dr Rusbridge is a world leading authority on canine CMSM. She is based at Fitzpatrick’s Referrals, Godalming, Surrey, and the University of Surrey Veterinary School. More detailed information on Syringomyelia can be found at Dr Rusbridge’s website. Rod Russell’s US based Cavalier Health website.
You can also download the following PDF documents from this website:
Genetic studies of Chiari-like Malformation with Syringomyelia in the CKCS by Clare Rusbridge [PDF]
Treatment algorithm for Chiari-like Malformation with Syringomyelia [PDF]
A support group for owners of affected dogs (also run by Karlin Lillington) may be found here.
Publicity leaflet for the new official BVA KC CMSM MRI screening scheme for breeders may be seen here.
Syringomyelia (SM) is characterised by fluid filled cavities within the spinal cord. SM occurs secondary to obstruction of cerebrospinal fluid (CSF) especially if that obstruction is at the foramen magnum. The most common predisposing cause in the dog is Chiari-like malformation (CM). The primary clinical sign of CM/SM is pain, either due to obstruction of the CSF pulse pressure and/or a neuropathic pain syndrome due to damage to the spinal cord dorsal horn.
Chiari-like malformation (CM) is a condition characterised by disparity in size between the brain (too big) and the caudal fossa (too small) such that the cerebellum and brain stem are herniated into or through the foramen magnum.
The pathogenesis of canine CM/SM is not fully understood. An important contributory factor is thought to be the mismatch in size between the brain and skull volume. Studies in the Griffon Bruxellois have suggested that CM is characterised by a shortening of the basicranium and supraoccipital bone with a compensatory lengthening of the cranial vault especially the parietal bone. This has led to the hypothesis that the condition may be due to insufficiency of the bone and /or craniosynostosis of the lambdoid (occipitoparietal) and cranial base sutures. The precise pathogenetic mechanism of development of syringomyelia is much debated.
A popular theory is that obstruction of CSF flow results in relative increase in spinal cord pressure and decrease in pressure in the CSF space around the spinal cord, the consequence of which is repeated mechanical distention of the spinal cord. This in turn results in dilatation of the central canal and accumulation of tissue fluid which eventually coalesces into cavities. Almost all Cavaliers have CM. One of the enigmas of CM/SM is the difficulty of predicting or explaining which dogs with CM will subsequently develop SM. The cause of SM is a mismatch between brain and skull size. Cavaliers have a similar skull volume to other Toy breeds but more brain tissue within the skull. Skull volume is significantly smaller for CKCS with early onset SM. The volume of brain within the skull is greater for CKCS with SM, especially in those dogs with early onset SM. A large syrinx is associated with larger brain ventricles.
The CKCS is overwhelmingly overrepresented for cases of CM/SM. There is no colour or sex predisposition. As shortened skull is a risk factor, any breed with a degree of brachycephalism and/or miniaturization could potentially be predisposed to CM/SM. To date the condition has been also reported in King Charles spaniels, Griffon Bruxellois, Yorkshire terriers, Maltese terriers, Chihuahuas, Miniature dachshunds, Miniature/toy poodles, Bichon Frisé, Pugs, Shih Tzus, Pomeranians, Staffordshire bull terriers, Boston terriers, French bulldogs a Pekingese, a miniature Pinscher and a couple of cats. Not all dogs with SM have clinical signs. The presence of signs is correlated to the width of the syrinx and extent of spinal cord dorsal horn damage. Syrinxes can progressively expand and a dog which is asymptomatic in early life may eventually become painful. A proportion of CKCS without SM may have painful signs associated with CM only (as in the case of humans) The clinical course may be acute or run an extended course over several months or years. Dogs may be presented at any age. Prevalence of SM in CKCS: 25% at one year of age, rising to 70% on dogs over 6 years of age (Vet Record 22 December 2011)
The most important and consistent clinical sign of CM/SM is pain however this may be difficult to localise. Owners may describe postural pain; for example, affected dogs may suddenly scream and/or lie with the head on the ground between the paws after jumping up or during excitement. It is also common to sleep with the head in unusual positions, for example elevated. Discomfort often appears worse in the evening and early morning or when excited and can be associated with defaecation or may vary with weather conditions. Pain is positively correlated with syrinx width and symmetry i.e. dogs with a wider asymmetrical syrinx are more likely to experience discomfort, and dogs with a narrow syrinx may be asymptomatic, especially if the syrinx is symmetrical. Dogs with a wide syrinx may also scratch, typically on one side only, while the dog is walking and often without making skin contact, such behaviour is often referred to as an “air guitar” or “phantom” scratching. Dogs with a wide syrinx are also more likely to have scoliosis. In many cases the scoliosis slowly resolves despite persistence of the syrinx. SM may result in other neurological deficits such as thoracic limb weakness and muscle atrophy (due to ventral horn cell damage) and pelvic limb ataxia and weakness (due to white matter damage or involvement of the lumbar spinal cord by the syrinx). Seizures, facial nerve paralysis and deafness may also be seen; however, no direct relationship has been proven and this association may be circumstantial. CM alone appears to cause facial pain in some dogs with owners describing ear and facial rubbing/scratching. It has been proposed that CM and compression of the brain stem can result a pain syndrome.
Magnetic resonance imaging (MRI) is essential for diagnosis and determining the cause of SM. In the instance of CM/SM the cerebellum and medulla extend into or through the foramen magnum which is occluded with little or no CSF around the neural structures. The size of the cerebellar herniation is not correlated with severity. There is typically ventricular dilatation. SM is indicated by fluid-containing cavities within the spinal cord. The upper cervical and upper thoracic segments are typically most severely affected. Maximum syrinx width is the strongest predictor of pain, scratching behaviour and scoliosis; 95% of CKCS with a maximum syrinx width of 0.64cm or more will have associated clinical signs.
The main treatment objective is pain relief. The most common surgical management is cranial/cervical decompression (also described as foramen magnum or suboccipital decompression) establishing a CSF pathway via the removal of part of the supraoccipital bone and dorsal arch of C1. This may be combined with a durotomy (incision of the dura with/without incision of subarachnoid meninges) with or without patching with a suitable graft material. Cranial/cervical decompression surgery is successful in reducing pain and improving neurological deficits in approximately 80% of cases and approximately 45% of cases may still have a satisfactory quality of life 2 years postoperatively. However surgery may not adequately address the factors leading to SM and the syrinx appears persistent in most cases. The clinical improvement is probably attributable to improvement in CSF flow through the foramen magnum. In some cases scaring and fibrous tissue adhesions over the foramen magnum seem to result in re-obstruction and 25% to as many as 50% of cases can eventually deteriorate. This can be as early as 2 months postoperatively. Due to the persistence of SM and/or spinal cord dorsal horn damage it is likely that the post-operative patient will also require continuing medical management for pain relief and in some patients medical management alone is chosen because of financial reasons or owner preference. There are three main drugs used for treatment of CM/SM: drugs that reduce CSF production; analgesics; and corticosteroids (Treatment Algorithm). If the dog’s history suggests postural pain or discomfort relating to obstruction of CSF flow then a trial of a drug which reducing CSF pressure, e.g. furosemide, cimetidine or omeprazole, is appropriate. This can also be very useful if it is difficult to determine if the cause of discomfort is CM versus, for example, ear disease. CSF pressure reducing drugs may be sufficient to control signs in some dogs, but additional analgesics are likely to be necessary for an individual with a wide syrinx. In this circumstance we suggest that non steroidal anti-inflammatory drugs are the medication of first choice partly because there are several licensed products. However, for dogs with signs of neuropathic pain, i.e. allodynia and scratching behaviour (suspected dysesthesia); a drug which is active in the spinal cord dorsal horn is more likely to be effective. Because gabapentin has established use in veterinary medicine we suggest that this is the drug of first choice but amitriptyline or pregabalin may also be suitable. Corticosteroids are an option if pain persists or where available finances prohibit the use of other drugs. Because the mechanisms of development of neuropathic pain are multifactorial, appropriate polypharmacy is likely to be more effective than treatment with single agents. The dog’s activity need not to be restricted but owner should understand that dog may avoid some activities and grooming may not be tolerated. Simple actions, for example raising the food bowl and removing neck collars, can also help. Treatment algorithm for Chiari-like Malformation with Syringomyelia [PDF]
Prognosis for CM/SM managed medically is guarded especially for dogs with a wide syrinx and/or with first clinical signs before 4 years of age. Study of a small case series (14 CKCS) managed conservatively for neuropathic pain suggested that 36% were eventually euthanatized as a consequence of uncontrolled pain. However 43% of the group survived to be greater than 9 years of age (average life expectancy for a CKCS is 10.7 years). Most dogs retain the ability to walk although some may be significantly tetraparetic and ataxic.
Official BVA/KC MRI Scheme
It is recommended that all breeders screen their stock for syringomyelia. Results will grade for CM and SM and will be used to generate Estimated Breeding Values (EBVs) for SM. Precise recommendations for breeding and grading system are available to download [PDF].
Heart Disease (Mitral Valve Disease)
Heart Mitral Valve Disease (MVD), or more correctly, myxomatous mitral valve disease (MMVD) is the leading cause of death of Cavalier King Charles Spaniels throughout the world. MVD is a complex polygenetic disease which afflicts half of Cavaliers by the age of five and nearly all Cavaliers by age ten years, should they survive that long.
What is it?
MVD is a degeneration of the heart’s mitral valve, one of four sets of valves in a dog’s heart. As the mitral valve degenerates, the valve no longer fully closes after each pumping action, allowing some blood to flow backwards through it from the ventricle back into the atrium. As the condition worsens, more and more blood is able to backflow through the valve. In the final stages, the valve’s struts sometimes break, causing the valve to collapse completely. MVD results in congestive heart failure in the CKCS. Mitral valve disease is the most common heart disorder in older dogs of all breeds, affecting more than one third of dogs over 10 years of age. However, in the Cavalier, the prevalence of MVD is about 20 times that in other breeds, possibly reaching a life-threatening stage within as little as 1 to 3 years.
All Cavaliers should be screened for heart murmurs once a year from the age of one year. Once MVD is detected, its progression can be monitored with a stethoscope (auscultations), x-rays, and echocardiograms. If a heart murmur is detected, it should be confirmed in 3 to 6 months. Mitral valve murmurs are graded from the mildest and least audible, Grade 1, to the loudest and most turbulent, Grade 6. Most Cavaliers show a gradual progression in the loudness of the MVD murmur. The loudness of the murmur usually indicates the severity of the valve leak. The progression of mitral valve disease can be rapid or slow. In most Cavaliers, the disease shows a gradual progression in the loudness of the murmur and to more serious symptoms.
Grades 1 and 2 murmurs are usually subclinical but as MVD progresses the early symptoms shown are exercise intolerance, breathlessness, coughing, a distended abdomen, weight loss and fainting. Breathlessness is the most common sign, starting as excessive panting with exercise. Severe mitral valve disease can mean that a dog will have difficulty breathing even while at rest and will not tolerate even minimal exercise. A dog with end stage MVD suffers from a progressive deterioration of its quality of life, due to an inability to keep him free from fluid congestion, together with enlarged heart chambers, lethargy, collapse, and deterioration of its kidney and liver functions. At this stage no drug is able to remove enough of the fluids and increase the supplies of blood and oxygen to the heart, resulting in heart failure.
Canine mitral valve disease cannot be cured but treatment with drugs can alleviate symptoms and prolong good quality of life. Dogs with MVD should not be allowed to become overweight as this puts extra strain on the heart and extreme exertion should be avoided. Moderate MVD involves fluid and salt retention and such dogs are commonly treated with diuretics such as Frusemide. Dogs with severe mitral valve disease are now treated with pimobendan (Vetmedin). This relatively new drug (2007) has been shown to improve the quality of life for dogs suffering from chronic heart failure due to MVD. For a more detailed explanation of all aspects of mitral valve disease visit Rod Russell’s website on Cavalier health. Also visit the UK Cavalier Club’s website. Dr Brendan Corcoran’s research paper, ‘Understanding Mitral Valve Disease’ (March 2009) is recommended and is published on the Cavalier Club website. Further research is taking place at the Royal Veterinary College
MVD Breeding Protocol
The Breeding Protocol aimed at breeding away from early onset MVD can be downloaded here: [PDF]. Sadly, in 15 years of this protocol being in place the incidence of early onset MVD has not improved. It is still the case that 50% of Cavaliers have a heart murmur by the age of five, and still far too many Cavaliers suffer and die young because of it. This is because the voluntary code of practice is ignored by the majority of Cavalier breeders, who routinely breed their dogs under the age of two and a half years.
The official BVA / KC Heart Testing Scheme
This was promised in 2008 but despite many inquiries to the BVA and Kennel Club the Scheme has not yet been set up (ie by 2014)
Other Health Issues
Eye Disease (Multifocal Retinal Dysplasia, MRD)
This is a hereditary disease involving the defective development of the retina (innermost layer of the eye; it includes the light sensitive rods and cones which transmit impulses to the optic nerve). Defective retinal development results in linear folding of the sensory retina and the formation of rosettes composed of retinal cells. These abnormalities can result in severe visual impairment, although many dogs will have no obvious visual defect. It is essential that breeding dogs are screened under the BVA/KC eye scheme. DNA research into MRD is being undertaken by Claudia Hartley at the Animal Health Trust, who believes that the gene marker for MRD in Cavaliers will be the same as in Golden Retrievers. There is no reliable data available on the level of incidence of MRD in Cavaliers.
Cavaliers can suffer from congenital deafness which is present at birth and is due to a lack of formation or early degeneration of receptors in the inner ear. Cavaliers can also develop progressive hearing loss, which usually begins during puppyhood and progresses to profound deafness between the ages of three and five years. This is believed to be due to degeneration of the hearing nerve. There is no reliable data on the level of incidence of either of these ear diseases. A common ear disorder in Cavaliers is caused by a build up of mucoid material in the tympanic bullae. This is a viscous plug which fills the middle ear rather like ‘glue ear’ in children. Some vets refer to this as middle ear disease or primary secretory otitis media (PSOM). This condition is very common in Cavaliers and is thought to be linked to poor drainage (due to skull conformation) through the eustachian tube. In many cases this does not cause pain or discomfort for the dog but some experts believe that middle ear disease can cause outward signs of pain similar to Syringomyelia. More research is needed in this area and as far as I am aware, there are no attempts by breed clubs to tackle the problem of deafness and ear disease. However, BAER (brainstem auditory evoked response) testing is available and should be used by breeders to test their breeding dogs for hearing deficiencies prior to being bred. BAER testing should be conducted at the minimum age of two and a half years (as MVD and MRI screening), and at the low decibel intensity threshold of 30 dB, to ensure that hereditary deafness is not passed on to offspring.
Dry Eye / Curly Coat (Ichthyosis Keratoconjunctivitis Cicca)
Dry eye in conjunction with curly coat syndrome is unique to the Cavalier breed. Puppies may be identified at birth by the curly abnormality of the coat and extreme dryness of the skin. Such puppies need daily skin care, medicinal bathing and daily eye treatment to prevent ulceration and infection. Such dogs will have a lifetime of extreme discomfort and permanent eye damage and for this reason are usually euthanased shortly after birth. Following research at the Animal Health Trust (AHT), it is thought that the carrier rate for DECC is 30%. A DNA test is now available from the AHT and all breeding dogs should be tested. Dry eye can also exist on its own and is an immune mediated destruction of the tear glands. Initial symptoms include chronic redness of the eye and a viscous discharge. Early and regular treatment is needed to prevent damage to the cornea. Treatment is aimed at increasing tear production, applying artificial tears, and reducing bacterial infection and inflammation. Needless to say, dogs with dry eye should not be bred from.
Episodic Falling Syndrome (Paraxysmal Hypertonicity Disorder), EFS
Episodic falling is a syndrome of muscle stiffness or collapse that occurs in the Cavalier. In severe cases, the front legs curl up over the head, hind legs become rigid and jaws are clenched. The dog’s quality of life can become significantly affected as episodes can last for hours and happen several times a day. Chronic pain is also believed to be associated with EFS Research for EFS at the Animal Health Trust (AHT) has found that the carrier rate is 30%. A DNA test is now available at the AHT and all breeding dogs should be tested An excellent website on Episodic Falling in Cavaliers can be found here.
Chronic Pancreatitis (CP)
Cavaliers appear to have an increased risk of developing chronic pancreatitis (CP), which is a progressive inflammatory disease of the pancreas. This can result in recurrent vomiting and diarrhoea (although there are of course, many other causes of this apart from pancreatitis). In some dogs, eventually, when 90% of the pancreas has been destroyed by the inflammation, the dog will develop a deficiency of pancreatic enzymes (‘exocrine pancreatic insufficiency’ EPI) and/or a deficiency of insulin which is also produced by the pancreas. The latter results in diabetes mellitus, and it is likely that end stage chronic pancreatitis is the commonest cause of diabetes mellitus in the breed, although this has not yet been proved. Dogs which suffer from CP may show no obvious signs of recurrent mild to severe gastrointestinal upsets and/or abdominal pain. However, once they develop EPI, they start to lose weight in spite of good appetite, and also produce voluminous faeces. A dog can live without a pancreas, so the disease is often not fatal, but enzyme supplements in the food and insulin treatment will be necessary in the end stage. Sometimes, an acute bout of pancreatitis can, however, be fatal. Vets will recognize an acute bout of pancreatitis and provide appropriate treatment – but researchers are only just beginning to realise that this is could be just the ‘tip of the ice-berg’ and that Cavaliers often have serious, underlying chronic disease in their pancreas already. Pathology studies suggest it is very common in the breed – although under-recognised. Penny Watson at Cambridge University Vet School is investigating the disease, but the mode of inheritance is not yet known. If you are concerned that your dog may have chronic pancreatitis, Dr Watson would be very happy to give your vet advice and help as necessary. Studies into this disease are at a very early stage and calls will be put out for help and information as the study develops. Currently neither the Cavalier clubs, nor the Kennel Club have identified CP as a breed health problem. Patella luxation (slipping kneecap) The patella is anchored in place by ligaments and slides in a groove in the femur. If the groove is too shallow, the patella will slip out when the knee bends. When the patella slips out to the inside of the knee joint, its called medial luxation. When it slips out to the outside, its called lateral luxation. Surgery is needed to treat this condition. Colitis (frequent tummy upsets) Inflammation of the colon causing chronic diarrhea. Information on other Cavalier health issues and more details can be found at www.cavalierhealth.org.