Degenerative myelopathy is a degenerative disease of the spinal cord in older dogs. The insulation of the fibers that send signals from the brain to the legs is stripped away little by little. On average, after a time of 6-12 months, there may no signal at all.
The signs of DM vary, but most commonly, it starts with a dog dragging one foot. As the disease progresses, there is a loss of coordination (ataxia) and the legs become weaker. Dogs will have a difficult time running, walking, and then … even standing. There is no pain associated with DM, but dogs will, at some time, become paraplegic. The disease appears to move from the rear to the front and in some cases, the dog cannot move at all.
The only way to conclusively diagnose DM is through an autopsy. Herniated disks can cause hind leg weakness and so can tumors, cysts, infections and strokes. Those conditions might be identified through advanced diagnostic procedures such as an X-ray or MRI so a diagnosis of DM is usually made through elimination.
Unfortunately, there is no cure for DM at this time and there is no way to even stop the progression of the disease. The only thing you can do is help your dog deal with the disease. The American Boxer Club has an outstanding article about dealing with DM - click here to read it.
Researchers found a gene mutation that is associated with degenerative myelopathy and many breeders are testing their dogs and bitches in an effort to breed away from the disease. A good way to make sure the research continues is to donate to the American Boxer Charitable Foundation.
Source: Canine Diseases Genetic Network - University of Missouri College of Veterinary Medicine