Syringomyelia (SM) is a congenital or acquired intraspinal disease. It is a neurological disorder where a cyst or herniation, known as a syrinx, forms within the spinal cord and cause the flow of cerebrospinal fluid (CSF) to become obstructed and accumulate, causing symptoms which can range in dogs from “air” scratching, pain and limb dysfunction. The syrinx can be located anywhere on the spine but most commonly in dogs at the location of the foramen magnum (where the brain and spinal cord join).
When there is a malformation of the foramen magnum this is referred to as Chiari-like Malformation (CM) and may or may not be accompanied by Syringomyelia. CM refers to caudal fossa crowding a defect that causes a disruption of CSF at that area and have perhaps led to the misleading idea that Cavaliers have “exploding brains”. It is thought that the large majority of Cavalier King Charles Spaniels have the Chiari-like Malformation with only a small number developing and becoming symptomatic for SM; therefore, a natural deformity for the breed.
There are other primary conditions which can be accompanied by SM such as hydrocephalus and atlantoaxial subluxation and there are other conditions with similar symptoms that should be ruled out such as PSOM, allergies and other neurological problems.
Syringomyelia can be either acquired or congenital. If acquired, this would occur due to trauma, complications of surgery or disease such as a tumor and the syrinx would develop in the damaged segment of the spine and may expand causing difficulties. It is also possible that a difficult birth may cause damage in the neck/spine area resulting in the acquired form. If congenital, the condition would develop in the womb as a malformation
Both CM and SM were originally considered rare but with more advanced testing and imaging equipment it has been found to be more commonplace in dogs, humans and other species. Originally publicized to be a condition specific to the Cavalier King Charles Spaniel SM is seen more often in small breed dogs such as Brussel Griffons, Pomeranians, Maltese, Poodles (toy and minis), Chihuahua, Mini Dachshund, Bichon Frise, Shih Tzu in addition to the CKCS but has been found in larger breeds such as Bull Terriers, Labrador Retrievers and Weimaraners.
What are the symptoms?
The most common symptom of Syringomyelia in the Cavalier King Charles Spaniel is a hypersensitivity in the neck area resulting in an uncontrolled urge to scratch at the neck and shoulders (aka “air” or “guitar” scratching), quite often to the point that the dog will fall over. This scratching behavior is quite distinctive and hard to mistake for regular scratching. There is quite often discomfort and pain in the neck and ear areas. There may also be facial paralysis, progressive weakness in the limbs, loss of bladder and bowel control and scoliosis (curvature of the spine). The condition can be aggravated by excitement or stress.
In the congenital form symptoms are usually first seen from 6 to 18 months of age but depending upon the degree affected could manifest at any age. In the acquired form symptoms can be seen any time after the original injury or trauma to the spine.
Though the condition was recognized symptomatically earlier it has only been due to the advances in advanced imaging techniques through the use of Magnetic Resonance Imaging (MRI) that this disease has been understood and diagnosis been able to be confirmed.
The MRI is the leading diagnostic tool used in determining Syringomyelia. It has only been since 1993 that a functional MRI was developed and around 1996 when it was advanced enough and readily available to diagnose spinal conditions in dogs.
MRI images are formed by the combination of a strong magnetic field and radio wave interacting with the hydrogen protons in the body and then using a computer the information is collected and made into three dimensional pictures of the body. The MRI can then characterize and discriminate among the tissues using their physical and biochemical properties (water, fat, iron, blood and its breakdown products) allowing blood flow, cerebrospinal fluid (CSF) flow and contraction and relaxation of organs to be evaluated.
Using the MRI then allows the neurologist to study the spine for the presence of a syrinx or any other abnormality, such as a tumor which might obstruct the flow of the spinal fluid.
Treatment of SM
Mildly affected Cavaliers with the condition may require little to no treatment. More severely affected dogs may require a variety of treatments which can range from medications to relieve the symptoms to surgery.
Oral medications, such as corticosteroids, diuretics and narcotics are used to control swelling, CSF production and pain. Surgery to allow the cerebrospinal fluid to flow normally by placing a shunt may be considered for more severe cases.
The mode of inheritance is unknown though it is suspected that it is polygenic. At present testing for the condition prior to breeding is done through the use of an MRI machine.
Disadvantages of MRI as a testing tool for breeders:
1. The results are speculative. The interpretation of the findings of CM and syrinx are as yet unclear. As the disease is considered progressive a breedable age dog may be cleared under the current guidelines yet develop the condition at the later date.
2. The results do not tell if the scanned dog is a carrier and can reproduced the condition in its offspring.
3. Dogs must be under anesthetic to have the test performed. Anesthetic/sedation can be dangerous and some dogs have died having this test performed.
4. Expense – the cost of a single MRI scan can range from approximately $700 to $3,000 to perform and not affordable for many breeders