Syringomyelia
Chiari-like malformation (CM) is believed to play a major role in the cause of syringomyelia (SM) in cavalier King Charles spaniels. While some forms of SM are known to have other causes, this article focuses primarily upon its relationship with CM.
CM is a complex skull and craniocervical junction malformation associated with a short skull, that is common in some brachycephalic toy breed dogs and especially the cavalier (CKCS). The skull is too small for the brain and there is also overcrowding of the spinal cord in the upper neck vertebrae. In the CKCS, this situation is compounded due to the cavalier having a comparatively large brain. The cavalier appears to have a brain more appropriate for a bigger dog, about the size as that of a Labrador retriever.
This disproportion causes the brain, particularly the cerebellum, to squeeze through the foramen magnum – the hole at the back of the skull, in the occipital bone – partially blocking the flow of cerebrospinal fluid (CSF) down the spinal cord. This both causes pain and the creation of fluid which collects in pockets in the spinal cord, which is what SM is. CM can cause irreversible damage to the spinal cord, resulting in additional pain and other neurological disorders.
SM is an extremely serious condition in which on or more of these "syrinxes" or "syringes", develop within the spinal cord near the brain. It is also known as "neck scratcher's disease", because one of its common signs is scratching in the air near the neck. "Syringomyelia" is Latin for "cavity within the spinal cord".
SM is rare in most breeds but has become very widespread in cavalier King Charles spaniels, the Brussels Griffon (Griffon Bruxellois), and Chihuahuas. The number of diagnosed cases in cavaliers has increased dramatically since 2000. Researchers estimate that more than 95% of cavaliers have CM and over 50% may have SM. The severity and extent of syringomyelia also appear to get worse in each succeeding generation of cavaliers. It is worldwide in scope and not limited to any country, breeding line, or kennel, and experts report that it is believed to be inherited in the cavalier.
CM/SM seldom can be detected in young puppies, as symptoms of it usually are not evident before the age of six months or years later.
Dogs diagnosed with CM and SM may have no symptoms at all. If CM-affected dogs do have symptoms, they indicate pain (CM-P). The most common ones are: (a) vocalisation (barking, whining, moaning) particularly when being picked up under the chest or when changing position; (b) head scratching or head rubbing; (c) reduced activity, such as a reluctance to climb stairs or jump; (d) behavioural changes, such as becoming timid, anxious, or aggressive; and/or (e) touch aversion.
SM-affected dogs may be asymptomatic if the syrinx is small and does not interfere with the spinal cord. Larger syrinxes -- those having a diameter of 4 mm or more -- can damage the spinal cord and cause symptoms such as phantom scratching, scoliosis, and weakness in the limbs.
Pain is the most important clinical sign of CM. Symptoms may vary widely among different dogs, but the earliest sign often is that the dog feels a hypersensitivity in its neck area, causing in some an uncontrollable urge to scratch at its neck and shoulders. Then usually follows severe pain around its head, neck, and shoulders, causing it yelp or scream. 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.
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 anaesthetised.
CM is a complex skull and craniocervical junction malformation associated with a short skull, that is common in some brachycephalic toy breed dogs and especially the cavalier (CKCS). The skull is too small for the brain and there is also overcrowding of the spinal cord in the upper neck vertebrae. In the CKCS, this situation is compounded due to the cavalier having a comparatively large brain. The cavalier appears to have a brain more appropriate for a bigger dog, about the size as that of a Labrador retriever.
This disproportion causes the brain, particularly the cerebellum, to squeeze through the foramen magnum – the hole at the back of the skull, in the occipital bone – partially blocking the flow of cerebrospinal fluid (CSF) down the spinal cord. This both causes pain and the creation of fluid which collects in pockets in the spinal cord, which is what SM is. CM can cause irreversible damage to the spinal cord, resulting in additional pain and other neurological disorders.
SM is an extremely serious condition in which on or more of these "syrinxes" or "syringes", develop within the spinal cord near the brain. It is also known as "neck scratcher's disease", because one of its common signs is scratching in the air near the neck. "Syringomyelia" is Latin for "cavity within the spinal cord".
SM is rare in most breeds but has become very widespread in cavalier King Charles spaniels, the Brussels Griffon (Griffon Bruxellois), and Chihuahuas. The number of diagnosed cases in cavaliers has increased dramatically since 2000. Researchers estimate that more than 95% of cavaliers have CM and over 50% may have SM. The severity and extent of syringomyelia also appear to get worse in each succeeding generation of cavaliers. It is worldwide in scope and not limited to any country, breeding line, or kennel, and experts report that it is believed to be inherited in the cavalier.
CM/SM seldom can be detected in young puppies, as symptoms of it usually are not evident before the age of six months or years later.
Dogs diagnosed with CM and SM may have no symptoms at all. If CM-affected dogs do have symptoms, they indicate pain (CM-P). The most common ones are: (a) vocalisation (barking, whining, moaning) particularly when being picked up under the chest or when changing position; (b) head scratching or head rubbing; (c) reduced activity, such as a reluctance to climb stairs or jump; (d) behavioural changes, such as becoming timid, anxious, or aggressive; and/or (e) touch aversion.
SM-affected dogs may be asymptomatic if the syrinx is small and does not interfere with the spinal cord. Larger syrinxes -- those having a diameter of 4 mm or more -- can damage the spinal cord and cause symptoms such as phantom scratching, scoliosis, and weakness in the limbs.
Pain is the most important clinical sign of CM. Symptoms may vary widely among different dogs, but the earliest sign often is that the dog feels a hypersensitivity in its neck area, causing in some an uncontrollable urge to scratch at its neck and shoulders. Then usually follows severe pain around its head, neck, and shoulders, causing it yelp or scream. 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.
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 anaesthetised.
