Degenerative Myelopathy

These next few weeks I am going to steer away from the orthopedic realm and delve into some neurologic conditions.

Degenerative myelopathy (DM) is a pain free, progressive, degenerative disease of the spinal cord. It is similar to amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease in humans). DM occurs most commonly in German Shepherd Dogs, Pembroke Welsh Corgis, Chesapeake Bay Retrievers, and Boxers with the mean age of onset being 9 years old. The suggested cause of DM is inherited as it has been found to be correlated with a mutation in the SOD1 (superoxide dismutase 1) gene. Testing via cheek swab is suggested for at risk breeds showing clinical signs. If two copies of the mutated gene are present, the dog is at risk for DM. If only one mutation is present, the dog is not at risk but is a carrier and should not be bred. If no mutation is present they are not at risk for DM. It is important to note that this test does not confirm DM as a diagnosis, but it can rule it out, in which case other diagnoses such as spinal injury, spinal tumor, lumbosacral stenosis, fibrocartilaginous embolism, myasthenia gravis, and discospondylitis could be explored. If the dog has two copies of the mutated gene along with clinical signs found on exam and other differential diagnoses are ruled out by testing for those then it is presumed to be DM. DM is not painful, so this may help in diagnosis, if there is pain, it is from another cause. Most large breed dogs progress to non ambulatory paraparesis within 6-9 months of onset of clinical signs.

Below, I have broken down the symptoms of disease in early, mid, and late stages.

Early phase:

• hind limb ataxia (decreased coordination), usually seen as swaying, staggering, and scuffing of the hind limbs

• hind limb and core weakness initially sometimes worse on one side

• mild spastic paresis in the hind limbs

• worn nails on the hind limbs

• reflexes are normal to exaggerated in the hind limbs

Mid phase:

• paraparesis (partial paralysis) of the hind limbs

• mild incontinence

• front limbs may start to become weak

Late phase

• weakness now affects the front limbs and is more symmetrical than early in the disease

• loss of reflexes in the hind limbs

• muscle atrophy

• non ambulatory and incontinent

• swallowing difficulties and an inability to bark

Treatment:

There is no cure for DM and the long term prognosis is poor. Rehabilitation is crucial to delay progression and maximize the dog’s quality of life and independence. Laser therapy has been shown to delay the degeneration of the nervous system. The Kathmann Protocol has been proven to extend the dog’s life. In 2006 the study reported survival data from 22 DM affected dogs that received varying degrees of physical therapy (PT). Dogs that received intensive PT had significantly longer survival times (mean 255 days) compared with the moderate (mean 130 days) and no (mean 55 days) PT. This protocol uses active exercises, passive exercises, massage, hydrotherapy, and paw protection for treatment. Physical therapy is also important to help provide education to the owners as the disease progresses. Rehabilitation providers can help owners with recommendations for equipment such as slings, harnesses, or wheelchairs as mobility declines as well as the education on home management strategies for improved quality of life at home.

Things to remember:

• Avoid over exertion (no high intensity exercise, long walks or hikes, or sprinting)

• Low intensity, higher frequency activities are better (5-10 minutes 5x/day rather than 45-60 min all at once)

• Controlled leash walking

• Home exercises as prescribed by your rehab provider

• There aren’t really any activity restrictions (other than over exertion), you want to maintain the highest level of functional mobility while avoiding fatigue.

DM is a very unfortunate diagnosis, but dogs can maintain a good quality of life for some time with the right rehab and commitment of the owners.

References:

Platt, Simon & Olby, Natasha. (2019). BSAVA Manual of Canine and Feline Neurology (4th edition). British Small Animal Veterinary Association

Millis, Darryl L. & Levine, David. (2014). Canine Rehabilitation and Physical Therapy (2nd edition), Elsevier

Zink, Chris & Van Dyke, Janet B. (2018). Canine Sports Medicine and Rehabilitation (2nd edition), WILEY Blackwell

Next week: Geriatric Onset Laryngeal Paralysis and Polyneuropathy (GOLPP)