Degenerative myelopathy 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. The affected dog will wobble when walking, knuckle over or drag their 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 6 months to 2 years before dogs become paralyzed. 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 legs. Another key feature of DM is that it is not a painful disease.
Degenerative myelopathy begins with the spinal cord in the middle back region. If we look under the microscope at that area of the cord from a dog that has died from DM, we see degeneration of the white matter of the spinal cord. The white matter contains fibers that transmit movement commands from the brain to the limbs and sensory information from the limbs to the brain. This degeneration consists of both demyelination (stripping away the insulation of these fibers) and axonal loss (loss of the actual fibers), and interferes with the communication between the brain and limbs. Recent research has identified a mutation in a gene that confers a greatly increased risk of developing the disease. The dogs homozygous for the mutation are at-risk for developing DM and will contribute one chromosome with the mutant allele to all of their offspring. The heterozygotes are DM carriers that are unlikely to or rarely will develop clinical DM but could pass on a chromosome with the mutant allele to half of their offspring. The SOD1 DNA test is of potential use to dog breeders wishing to reduce the incidence of DM in the breed or line.
There are no treatments that have been clearly shown to stop or slow progression of DM. Although there are a number of approaches that have been tried or recommended on the internet, no scientific evidence exists that they work. Dogs that received intensive physiotherapy had significantly longer survival times compared to dogs that received moderate or no physiotherapy. Physiotherapy and principles of physical rehabilitation may improve the quality of life for the DM affected pet and pet owner. Overall, the long term prognosis of DM is poor. The quality of life of an affected dog can be improved by measures such as good nursing care, physical rehabilitation, pressure sore prevention, monitoring for urinary infections, and ways to increase mobility through use of harnesses and carts.