King Charles Spaniel brain
What is Syringomyelia?
Syringomyelia is a condition whereby fluid filled cavities develop within the spinal cord. Some refer to SM as "neck scratcher's disease" because scratching in the air near the neck is a common sign.
What causes it?
Syringomyelia is a consequence of an obstruction to cerebrospinal fluid (CSF) flow. In the normal mammal, the CSF around the brain shunts back and forth with the arterial pulse. If this rapid efflux and influx is obstructed then the pressure wave is transmitted down the spinal cord distending it below the blockage. This results in the formation of a cavity or syrinx. Syringomyelia can occur from any blockage in the subarachnoid space (space containing CSF around the brain and spinal cord). However, the most common cause is the cerebellum within the foramen magnum (i.e. the back of the brain poking though the hole at the back of the skull). The cerebellum is pushed (herniated) out the skull because there is not enough space since the volume of the back of the skull (occipital bone) is too small. This condition occurs in many small breeds but is common in the cavalier King Charles spaniel (CKCS) (conservative estimates at least 50% of the breed although only a proportion are severe enough to have clinical signs). It is similar to the human condition Chiari malformation (some vets refer to it as Arnold Chiari syndrome which can be confusing as the original description by Arnold was of syringomyelia associated with spina bifida and this is not the case in the CKCS).
What are the clinical signs of syringomyelia?
By far the most important sign of syringomyelia is pain. This is most commonly localised to the neck region but may be difficult to define or intermittent. Owners often report that their dog is worse at night; when first getting up; during hot or cold temperature extremes; when excited; or related to posture e.g. preferring to sleep with their head elevated. They may seem to be overly sensitive to touch on one side of the neck / ear / shoulder / sternum. In addition some affected dogs scratch at one area of the shoulder, ear, neck or sternum. This is typically one side only, while the dog is moving and sometimes without making skin contact Some dogs, more commonly younger patients, develop a scoliosis (twisted spine). Some severe cases may have other neurological deficits such as fore and hindlimb limb weakness and ataxia (wobbliness). Facial nerve paralysis, deafness and seizures have also been associated with the condition but a link has yet to be proven.
What age of dog is affected?
Clinical signs of syringomyelia secondary to occipital hypoplasia are usually recognized between 6 months and 3 years of age. However, dogs of any age may be presented and dogs with more severe disease tend to be presented before two years of age.
Do the signs get worse?
Progression of the disease is very variable. Some dogs have the tendency to scratch with mild pain only and other neurological signs, such as paresis, never or very slowly develop. Others can be severely disabled by pain and neurological deficits within 6 months of the first signs developing. A small syringomyelia may also be found as an incidental finding, with no recognised clinical signs, in the investigation of another neurological disease.
Are there any diseases with similar signs to syringomyelia?
The main diseases to rule out are other causes of neck pain e.g. disc disease (uncommon in dogs less than two years of age); CNS inflammatory diseases and other malformations. If scratching or face rubbing is the main sign then skin disease should be eliminated.