Degenerative myelopathy
Dogs with degenerative myelopathy (formerly chronic degenerative radiculomyelopathy, CDRM) develop progressive weakness, wobbliness, and incontinence. Within two years of diagnosis, most dogs die or are put to sleep from complications of the disease.
There is a tendency for the condition to affect middle aged to elderly adult dogs (5-11 years with a median age of 9 years), regardless of gender. German shepherds, Boxers, Chesapeake Bay retrievers, Rhodesian ridgebacks and Pembrokeshire Welsh corgis are among the most commonly affected dog breeds. Although the condition can affect dogs of any breed, medium to large breed dogs are more likely to be affected.
As dogs typically develop signs of disease when they are middle-aged or older, the condition can be mistaken for arthritis or other conditions affecting the lower back and rear legs.
What causes degenerative myelopathy?
Degenerative myelopathy (DM) is a neurodegenerative disease in which there is a slow loss of nerve fibres in the spinal cord without any inflammatory, infectious or cancerous cause.
We suspect a strong genetic component to this condition; however, veterinarians are uncertain of the underlying cause. The genetic cause of ALS (amyotrophic lateralising sclerosis) in humans is known, and studies in dogs have identified a similar mutation.
What are the signs of degenerative myelopathy?
In most cases, the spinal cord is affected in the lower back. The most common symptoms of DM are weakness (paraparesis) and wobbliness/drunkenness (ataxia) in the hind limbs. It is common for the weakness to be more severe on one side. It is important to note that pain is not one of the key characteristics of the condition.
There is a possibility that the condition may progress in the spinal cord, resulting in urinary incontinence, weakness in the front limbs, and even difficulty swallowing, barking, and moving the jaw with time.
While there are some dogs with the condition who progress very slowly over time (years), there are others whose condition progresses rapidly, with weakness causing severe quality of life issues in less than a year.
How can I diagnose degenerative myelopathy?
A biopsy of a tissue sample from the spinal cord is required in order to make a definitive diagnosis of this condition. It is unfortunate that a spinal cord biopsy is never performed since this is an extremely important structure whose removal will result in paralysis.
Therefore, we combine physical examination findings with diagnostic imaging to arrive at a diagnosis. DM is often mimicked by other spinal cord disorders, including slipped discs (disc protrusions) and spine tumours. It is therefore of the utmost importance to investigate and exclude other potential causes of spinal cord disease. Slipped discs usually cause pain, but an MRI scan is usually required to rule out this possibility, as well as other possibilities, such as a spinal tumour. Rarely, a patient may suffer DM and disc protrusions simultaneously, complicating the diagnosis.
There is a genetic test available for the condition, but it is important to be aware of its limitations. Positive results indicate a dog has the potential to develop the condition, but may not actually develop it (we refer to this as incomplete penetrance). Even if the test is negative, the condition cannot be completely ruled out, because some dogs have been found to suffer from the disease without the specific mutation being detected. This test is rarely recommended by us.
Veterinary neurologists may sometimes recommend other tests such as spinal fluid collection via lumbar puncture (to exclude meningitis) or electrical nerve and muscle testing.
Can degenerative myelopathy be treated?
Unfortunately, since this is a genetic disorder, there is no specific treatment available. The treatment of this condition has not been studied over a long period of time, but it appears that drugs, such as steroids, do not assist in slowing its progression.
Only intensive physical therapy and hydrotherapy have been shown to slow the progression of the disease. It has been demonstrated that these treatments can improve the quality of life for DM-affected pets as well as their owners.
Will a dog recover from degenerative myelopathy?
Unfortunately, the prognosis for DM is not generally considered to be good. Despite treatment efforts, it is likely that the condition will progress over time. There is a likelihood that large breed dogs with this diagnosis will lose their ability to walk within a year of diagnosis, although some dogs may remain functional for a longer period of time. Smaller breed dogs have been reported to progress very slowly (2+ years) and may be easier to care for. In many cases, affected dogs are euthanased before the disease reaches an advanced stage.