Degenerative myelopathy (DM) is a poorly understood, progressive neurodegenerative disease seen in many dog breeds. Onset of the disease is typically is seen in dogs age 8 to 14.
Degenerative myelopathy begins with the spinal cord in the chest. The degeneration is two-fold: demyelination, i.e. the stripping away of the protective covering (myelin sheath) that surrounds nerve fibers in the spinal cord, and interference in the communication between the brain and the limbs.
The progression of the disease is variable and can span anywhere from 6 months to 2 years. In the early stages, there is a progressive weakness of the hind limbs with toe dragging and knuckling over, resulting in stumbling, worn nails, scuffling of the hind feet, and wear on the inner digits of the rear paws.
As the disease progresses, there is crossing of the hind legs and mild loss of side-to-side hip control, which becomes moderate, then severe to the point of loss of hip control. In the late stages, there is pelvic limb paralysis, urinary and fecal incontinence and even thoracic limb involvement. A key feature of the disease is that it is not painful.
DM is a diagnosis of elimination. Once other causes of weakness—such as herniated disks, tumors, cysts, infections, stroke and injury—are eliminated using diagnostic tests such as MRI, the presumptive diagnosis is DM.
While no treatments have been definitively shown to slow or stop the progression of DM, supportive treatment such as exercise, massage, physical rehabilitation, pressure sore prevention, and increased mobility through the use of harnesses and carts may increase the quality of life of affected animals.
Recent research has shown that a mutation in the SOD1 gene is a risk factor for developing degenerative myelopathy in dogs. Mutations in this same gene are also associated with familial Amyotrophic Lateral Sclerosis—also called ALS or Lou Gehrig's disease—in people.
The DNA test now available for use by veterinarians, breeders and owners through the Orthopedic Foundation for Animals (OFA) identifies dogs that are clear, those who are carriers, and those who are at much higher risk for developing DM. Dogs with 2 copies of the mutation (testing “affected”) are AT RISK for developing DM at some point in their lives—but may not develop it. Dogs that test “carrier” (one mutant copy and one normal copy) or “clear” (two normal copies) are highly unlikely to develop DM.
Some websites that may be helpful in learning more about this disease, along with support groups, include: