What is degenerative myelopathy?
Degenerative myelopathy (DM), also known as chronic degenerative radiculomyelopathy (CDRM) or German shepherd degenerative myelopathy, is a disease that affects the spinal cord, resulting in slowly progressive hind limb weakness and paralysis.
The symptoms result from degeneration of the white matter of the spinal cord. DM is like some forms of human amyotrophic lateral sclerosis (ALS), more commonly known as Lou Gehrig’s Disease.
The exact cause of DM is unknown. In its early stages, the symptoms of DM resemble those of osteoarthritis (arthritis), which often occurs secondary to hip dysplasia in many large breed dogs, making diagnosis challenging.
In later stages of the disease, progressive weakness and ataxia (wobbling, stumbling) distinguish it from osteoarthritis of the hip joints. Other possible reasons a dog might have these symptoms include spinal injuries, spinal tumors, lumbosacral stenosis, fibrocartilaginous embolism, myasthenia gravis, and discospondylitis.
What are the clinical signs?
Early clinical signs include:
- The hind paws "knuckle" or turn under so that the dog walks on its knuckles, especially when turning.
- The dog's hindquarters appear to sway when standing still.
- The dog falls over easily when pushed from the side.
- The hind feet seem to scrape the ground when walking and sometimes the top surface of the feet become hairless and irritated from repeated trauma.
- The dog has difficulty getting up from a lying position.
As the condition progresses and the spinal cord deteriorates, these symptoms worsen, eventually progressing to paralysis of the hind end.
What breeds are most affected?
A genetic mutation, SOD-1, has been identified as a major risk factor for DM. DM is considered a disease of middle-aged to older dogs including German shepherds, German shepherd crosses, Siberian huskies, and collies. Several other breeds have been identified as at risk for developing DM, including Bernese mountain dog, boxers, Chesapeake Bay retrievers,
Golden retrievers, Kerry blue terriers, miniature poodles, Nova Scotia duck tolling retrievers, pugs, Rhodesian ridgebacks, standard poodles, Pembroke corgis, Cardigan Welsh corgis, and wirehaired fox terriers). DM has been identified in more than 24 different breeds to date.
At what age does DM typically occur?
The condition is most common in middle-aged to older dogs, ranging from 4-14 years. It has been reported in young dogs on rare occasions.
What causes DM?
The exact cause of DM is unknown, although a genetic mutation is highly suspected. DNA testing through the Orthopedic Foundation for Animals can identify:
- dogs that are clear of DM (two normal copies of the gene),
- dogs that are carriers (one normal copy of the gene and one abnormal copy), and
- dogs at a much higher risk for developing DM (two copies of the mutated gene).
DM is an autosomal recessive genetic disease, meaning inheriting one or two copies of the gene (SOD1) increases the risk of developing the disease. However, not all dogs who carry these genes, even both copies, will develop DM. Other factors, both genetic and environmental, are believed to contribute to developing DM. There is still much to be discovered about DM in dogs and its causes. At-risk breeds should be tested for the SOD-1 mutation prior to breeding to avoid passing on the abnormal gene.
How is DM diagnosed?
This disease is suspected based on breed, medical history, physical examination, and diagnostic tests. X-rays and other spinal imaging techniques rule out other problems such as hip dysplasia and chronic arthritis, most often during the initial stages of DM. If one of these other problems is also present, it can contribute to the patient’s loss of function of the hindquarters.
Other tests that may be conducted include cerebrospinal fluid (CSF) analysis, tissue biopsies, and neuromuscular tests such as spinal cord evoked potentials (SCEPs). DNA testing for the SOD-1 mutation is recommended in any at-risk breed displaying clinical signs consistent with DM. Histopathology of the spinal cord is required for definitive diagnosis of DM, though this is only done post-mortem (after death). The diagnosis of DM is a challenging, often time-consuming endeavor, requiring many tests before a definitive diagnosis is made.
Are bowel and bladder problems associated with DM?
Bladder and bowel function are generally normal in the initial stages of DM. However, as the disease progresses to paralysis, the dog may develop urinary and fecal incontinence.
Is the condition painful?
Most affected dogs do not seem in pain, just very weak. If the dog appears to be in pain, there may be another condition such as arthritis complicating the condition. Affected dogs may become anxious or irritable due to loss of mobility as the condition progresses.
Is treatment possible?
There is no effective treatment for DM at present. Treatment of other concurrent problems, such as arthritis or hip dysplasia, may provide some relief. It is important to avoid obesity, so diet and exercise (walking and swimming) are vital components of treatment. The goal is to maintain the dog on its feet for as long as possible. Physical therapy has been shown to slow progression, prolong quality of life and preserve muscle mass. Any dog with DM should be kept as physically active as possible for as long as possible.
Although several medications and supplements have been recommended in the past, more recent findings suggest that an effective drug treatment still does not exist. Therapeutic laser or photobiomodulation therapy has shown promising results, but more research is still needed.
What is the prognosis?
Unfortunately, degenerative myelopathy is a progressive, incurable disease. Although bladder and bowel control are not affected initially, the dog has more difficulty controlling urination and defecation as the spinal cord continues to degenerate and the dog’s mobility becomes severely restricted. The nature and temperament of the affected dog determines whether a mobility aid such as a paraplegic cart will improve its quality of life in the short term.
The inevitable progression of this degenerative condition means that the symptoms will worsen over time. Your veterinarian will assess your dog’s circumstances and help you determine the most appropriate treatment options for your pet.
