Syringohydromyelia is also known as ‘Chiari-type malformation’ (a reference to the human disease) and ‘caudal occipital malformation syndrome’. Affected dogs develop a cyst-like lesion in their spine and this causes pain, and movement abnormalities. CKCS are genetically predisposed to develop this neurological abnormality but it can also be seen in other breeds. The diagnosis of syringohydromyelia can easily be confirmed using MRI which is now readily available for veterinary patients.
In the normal dog the brain and spinal cord are bathed in a fluid called cerebrospinal fluid (CSF). The term syringohydromyelia describes the presence of a fluid-filled cavity (called a syrinx) within the spinal cord. Cavalier King Charles Spaniels (CKCS) have an unusual conformation of the back of the skull (the occipital bone) and it is this that makes them particularly prone to developing the cavity in the spinal cord.
Because of the conformational abnormality the caudal part of the brain (cerebellum) doesn’t have enough room to develop inside the occipital bone. The cerebellum is therefore pushed through the hole at the base of the skull (where the spinal cord leaves the skull). This creates a pressure point, causing an abnormal flow of CSF from the brain to the spinal cord. With time this flow disturbance can result in the formation of a syrinx. In some dogs, it can also cause a build up of fluid in the brain called hydrocephalus.
Clinical signs can vary widely between dogs and there does not appear to be any relationship between the severity of syringohydromyelia and the severity of the clinical signs.
Affected animals show twisting of the neck (scoliosis), a stiff front limb gait, scratching of the neck and shoulder region, intermittent neck pain, loss of muscles in the neck, weakness or lameness of the front limbs. Signs typically appear in dogs before 6 years of age and get worse with age. The condition has been reported in puppies as young as 12 weeks.
However it is possible to find the changes of syringohydromyelia on MRI in dogs that have no clinical signs and similar clinical signs may be seen in dogs that have other neurological diseases.
The best way to diagnose syringohydromyelia is by means of MRI scanning. The abnormal bone conformation of the skull can be seen well with a CT scan (which is better designed to evaluate bone), but the information about the brain and spinal cord is less likely to show up on CT than with MRI. Special x-rays of the spine taken after injection of contrast agent may show up syringohydromyelia as a swelling in the spinal cord in the neck.
There is presently no gold standard treatment for dogs with syringohydromyelia. Both medical and surgical treatments have been tried, but in people surgical correction is thought to be the best treatment. In dogs, depending on the severity of the neurological signs and the age of the patient, medical management is usually recommended in first instance.
The most common drugs used in the management of the condition are prednisolone, acetazolamide and gabapentin. The first two are used to try to reduce CSF production and swelling of the spinal cord. Gabapentin is an anti-epileptic drug used in dogs and humans to treat pain caused by neurological disease as well as ‘pins and needles’ sensation. If there is no response to any of the drugs then a surgical treatment may be proposed.
At surgery the hole at the base of the skull is enlarged to relieve the pressure and restore a normal flow of CSF between the brain and the spinal cord. If surgery is performed in the early stages of the disease it may be possible to slow, or even stop, the development of the syrinx.
The course of syringohydromyelia is extremely variable between dogs, but once clinical signs are visible treatment is more likely to stabilise or slow the course of the disease. In general severely affected dogs showing signs before 4 years of age, will have a worse future than those that do not develop signs until later. As the cavity develops it causes damage to the spinal cord. This damage can never be repaired and a complete recovery is unlikely.
To date too few cases have been treated with surgery to be sure of the likely outcome of this in dogs. If you are thinking about having surgical management you should ensure your dog is assessed by a specialist neurologist as they will be best placed to advice on the best treatment in an individual case.
Because this is a genetic problem there is some hope that the disease could be eradicated by careful breeding. Researchers are searching for a genetic test that could identify affected dogs but at present the only diagnostic test available is MRI scanning. It is advisable that all CKCS should be screened with MRI after the age of two and half years to detect early lesions before breeding. Animals that show signs of disease must not be used for breeding.