Cornell Margaret and Richard Riney Canine Health Center

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Degenerative myelopathy

Overview 

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.  

Causes 

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.  

Breed predisposition 

Numerous dog breeds can be affected by DM, including, but not limited to the following: 

  • German Shepherd Dogs  

  • Boxers 

  • Pembroke Welsh Corgis 

  • Chesapeake Bay Retrievers  

  • Rhodesian Ridgebacks 

  • Bernese Mountain Dogs 

Clinical signs 

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: 

  • Difficulty rising  

  • Hind limb weakness  

  • Incoordination   

  • Muscle loss 

  • Scuffed toenails on hind limbs 

Diagnosis 

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. 

Treatment 

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 

Outcome 

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). 

Genetics 

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.