Degenerative myelopathy (DM) is a disease that affects the spinal cord in dogs, causing progressive muscle weakness and loss of coordination. It acts similarly to Lou Gehrig’s disease, or ALS (amyotrophic lateral sclerosis), in humans.
There is no cure for DM; however, routine physical therapy may delay the clinical progression of this disease.
DM is an inherited neurologic disease typically affecting dogs around eight years of age or older. It causes gradual muscle wasting and incoordination in the hind limbs, and then progresses to an inability to walk after six to twelve months. This muscle weakness may extend to the forelimbs in the late stages of the disease.
Certain genetic variations may increase a dog’s risk of developing DM, and environmental factors may also play a role.
Numerous dog breeds can be affected by DM, including, but not limited to the following:
German Shepherd Dogs
Pembroke Welsh Corgis
Chesapeake Bay Retrievers
Bernese Mountain Dogs
The clinical signs of degenerative myelopathy often start in one hind limb and then progress to include both. The clinical signs of DM may include:
Hind limb weakness
Scuffed toenails on hind limbs
There is no specific test to diagnose DM while a patient is living. Several tests may need to be performed to rule out other potential spinal cord diseases. Testing may include a neurological exam, blood work, X-rays, MRI or CT scan, and spinal fluid analysis.
Genetic testing will show if a patient has one or two copies of the variants associated with the development of DM.
There is no cure for DM, and management tactics include the following:
Physical therapy to slow the clinical progression and help maintain muscle mass
Maintaining a healthy weight
Using rugs, carpets or yoga mats on hardwood or tiled surfaces
Adding pet ramps or steps where necessary
Using a sling or harness to assist with walking and standing
Wearing booties to decrease damage to scuffed paws
Considering a wheelchair to support the hind limbs
Addressing any factors, like arthritis, that may also contribute to mobility issues
Degenerative myelopathy is a devastating disease. Often, dogs are humanely euthanized within six to twelve months after the onset of clinical signs, due to the debilitating loss of mobility caused by this disease. Without euthanasia, DM can progress for more than three years and lead to an inability to walk or even breathe normally.
However, even if an individual dog is genetically predisposed to developing DM, their overall chance of becoming clinically affected may still be low. It is therefore recommended that no drastic measures be taken without also considering a dog’s current clinical state (and general quality of life).
DM in most dog breeds is caused by a mutation in the SOD1 gene (SOD1A variant). Dogs with two copies of this variant are considered at a higher risk for developing DM, although it is not guaranteed that they will develop the disease.
A dog that is a carrier (possessing one copy of the variant) may still have a risk of developing DM, but generally, the progression of the disease is significantly slower than a dog with two copies of the variant.
There are individual, breed-based differences that influence the age of onset. For example, there is a genetic modifier that causes an earlier onset of clinical signs in Pembroke Welsh Corgis. A second variant (SOD1B) is found only in Bernese Mountain Dogs, and so they should be tested for both the SOD1A and B variants to assess their risk of developing DM.