Canine Degenerative Myelopathy

Canine degenerative myelopathy or DM is a progressive disease of the spinal cord in older dogs.  The disease has an insidious onset typically between 7 and 14 years of age.  It begins with a loss of coordination (ataxia) in the hind limbs.  As of July 15, 2008 the mutated gene responsible for DM has been found present in 43 breeds including German Shepherds, Boxers, Chesapeake Bay Retrievers, Rhodesian Ridgebacks, and both breeds of Welsh Corgis.  The disease is chronic and progressive, and resulting in paralysis.

The myelin is an insulating sheath around neurons in the spinal cord.  One proposed cause of degenerative myelopathy is that the immune system attacks this sheath, breaking it down.  This results in a loss of communication between nerves in lower body of the animal and the brain.

Symptoms:
Degenerative myelopathy is a progressive disease of the spinal cord in older dogs. The disease has an insidious onset typically between eight and fourteen years of age. It begins with a loss of coordination in the hind limbs. The affected dog will wobble when walking, knuckle over or drag its feet.  This can first occur in one hind limb and then affect the other.  As the disease progresses, the limbs become weak and the dog begins to buckle and has difficulty standing.  The weakness gets progressively worse until the dog is unable to walk.  The clinical course can range from six months to one year before dogs become paraplegic.  If signs progress for a longer period of time, loss of urinary and fecal continence may occur and eventually weakness will develop in the front limbs.  Another key feature of DM is that it is not a painful disease.

Testing:
The Orthopedic Foundation For Animals has a DNA test that can be purchased to see if your dog carries the mutated genes for DM.  The test is for any dog but is only recommended for certain breeds. The test consists of a cheek swab (using something similar to a Q-tip to swab the inside of the cheek to submit for testing).

The test checks for the mutated gene that will tell if your dog may be affected by degenerative myelopathy, if it is a carrier, or if it is unaffected.  Dogs that A/G or G/G are very UNLIKELY to develop DM.  However, dogs that A/A are LIKELY to develop clinical signs of DM at some point as they age.  For a more detailed explanation of how to understand the DNA results please visit the following Canine Genetic Diseases Network (CGD).

Causes:
The aetiology of this disease is unknown. Recent research has shown that a mutation in the SOD1 gene is a risk factor for developing degenerative myelopathy in several breeds.  Mutations in SOD1 are also associated with familial amyotrophic lateral sclerosis (Lou Gehrig’s disease) in people.

Known causes of spinal cord dysfunction should be excluded before accepting the diagnosis of degenerative myelopathy; disc disease (protrusions) or spinal cord tumours can cause compression of the spinal cord with similar signs to degenerative myelopathy.

Treatment: 
Degenerative myelopathy is a non-reversible, progressive disease that cannot be cured.  There are no treatments that have been clearly shown to stop or slow progression of DM.