Degenerative Myelopathy in Dogs

What is Canine Degenerative Myelopathy?

Degenerative Myelopathy (DM), also called chronic degenerative radiculomyelopathy (CDRM), is a genetic condition in dogs. It affects their spinal cord and results in progressive hindlimb weakness and paralysis, ultimately limiting the dog’s mobility. This disease is believed to be caused by a genetic mutation found in the genome of some dogs.

The dog must have 2 copies of the mutated gene for this disease (superoxide dismutase 1 or SOD-1) to develop degenerative myelopathy. Dogs with only 1 copy of the mutated gene are considered carriers and can pass the mutation to their puppies if they’re mated to another carrier.

The disease causes degeneration of the white matter of the spinal cord, causing mobility problems. Degenerative myelopathy is often likened to some forms of ALS (amyotrophic lateral sclerosis) in humans, more commonly known as Lou Gehrig’s Disease. Degenerative myelopathy can be seen in dogs 4 years and older, but older dogs over 8 years of age are most commonly affected. Symptoms of the disease usually start as mild mobility problems that become progressively severe over time.

What breeds are commonly affected by degenerative myelopathy?

While any dog can potentially develop degenerative myelopathy, some breeds are more predisposed to the disease compared to others. German Shepherds are infamously known to be highly predisposed to the condition, with as much as 2% of the entire breed population reported to be affected by the disease according to some studies.

Other breeds that are predisposed to degenerative myelopathy include Pembroke and Cardigan Welsh Corgis, Boxers, Wire Fox Terriers, Golden Retrievers, Great Pyrenees, Poodles, Pugs, Rhodesian Ridgebacks, Shetland Sheepdogs, and American Eskimo Dogs.

Symptoms of Canine Degenerative Myelopathy

The initial signs of canine degenerative myelopathy are subtle and often resemble osteoarthritis in dogs, which can make detection and diagnosis difficult. The onset of signs usually develops in dogs 8 years and older, but dogs as young as 4 years can be affected.

Early signs of the disease include:

• Swaying of the hips and hindlimbs when the dog is walking
• Difficulty standing up
• “Knuckling” of hind paws especially when turning
• Easily falling over when pushed from the side
• Scraping of the hind paws, resulting in irritation and hair loss from the repeated friction and trauma

In later stages of degenerative myelopathy, symptoms progress to paralysis of the back legs. Wobbling and stumbling are seen in affected dogs, which eventually progresses to the inability to stand on hind legs even when lifted or supported. There’s often loss of bladder and bowel control as the disease progresses and eventually, all limbs become weak resulting in paralysis of all legs. In severe cases, swallowing difficulties may also be observed. Dogs affected by this disease do not seem to show signs of pain due to spinal paralysis.

How is canine degenerative myelopathy diagnosed?

As mentioned, the initial symptoms of degenerative myelopathy closely resemble other musculoskeletal diseases which can make the diagnosis in the early stages of the disease particularly difficult. A thorough physical exam along with diagnostic imaging tests such as radiographs, CT, and MRI scans are needed to rule out other possible causes of hind limb weakness.

Cerebrospinal fluid (CSF) analysis and spinal cord biopsy may also be performed but are not routinely done in cases of hindlimb weakness in dogs. A tentative diagnosis of degenerative myelopathy is typically made after other possible causes of hindlimb weakness are ruled out.

Genetic testing can be done to check for the SOD-1 gene for a definitive diagnosis of canine degenerative myelopathy. This is often recommended for breeds that are highly predisposed to the condition.

Treatment Options for Dogs with Degenerative Myelopathy

Unfortunately, there is no cure for degenerative myelopathy in dogs. The main goal of treatment is to help control the symptoms of the disease and improve the dog’s quality of life. Since dogs affected with the disease don’t feel pain, medications to manage pain are often not needed unless there are concurrent conditions like osteoarthritis or hip dysplasia.

Lifestyle measures such as daily exercise and a proper diet to avoid excessive weight gain are important in managing the symptoms of the disease. Physical therapy in later stages can help prolong a dog’s quality of life and preserve muscle mass even as the limbs start to become weak. Supplements and medications such as Vitamins B, C, and E, N-acetylcysteine, and prednisone have been shown to slow down the progression of the disease.

But the progressive and incurable nature of the disease will eventually render these treatment measures ineffective. Even with consistent medication, physical activity, and proper diet, the disease will progress and cause severe weakness and complete paralysis of all limbs, starting with the back legs and eventually affecting the front limbs. When affected dogs eventually lose bladder control, manual expression a couple of times a day and urinary catheterization are needed to manage the urinary bladder and avoid complications of urine retention.

Unfortunately, canine degenerative myelopathy progresses very rapidly. Complete paralysis often occurs within 6 months to a year after a diagnosis is made. As the symptoms worsen, your veterinarian will assess your dog’s overall condition and quality of life and will help you determine the best treatment options and steps to take for your pet.

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