Imagine the confusion and fear you'd be feeling if you were approaching your middle years and suddenly developed difficulty walking. The same bewilderment hits middle-aged dogs who have a progressive nerve disorder known as degenerative myelopathy (DM). The disease causes the dog to slowly lose coordination of its hind legs, which also become increasingly weak. It's caused by a deterioration of structures within the spinal cord that are responsible for transmitting nerve impulses. This degeneration can occur anywhere along the spinal column, but usually affects the lower back.

Degenerative myelopathy is only found in dogs that are at least 5 years of age or older. The cause is not yet understood; although it's theorized that it could be related to an autoimmune response, in which the body immune system mistakenly attacks its own cells. As with all degenerative diseases, myelopathy develops slowly and is often mistaken for other conditions, such as hip dysplasia or spinal disc degeneration. A complete neurological exam, X-rays and an MRI can provide a definite diagnosis to distinguish true cases of DM.

The first symptoms normally are weakness and a lack of coordination in the dog's hind limbs. These are more noticeable when the dog is walking on a smooth surface, and one side may noticeably more affected than the other. Over time, the symptoms worsen until the dog is unable to walk. Many may begin urinating and defecating indoors or in inappropriate locations. This is not because they cannot control their bodily functions, but rather because they may be unable to walk to an appropriate spot or assume a normal position to relieve themselves.

DM is found almost exclusively in aging German Shepherds and German Shepherd crosses, although some other large breeds of dogs also can be affected. The disorder has been reported in Belgian Shepherds, Boxers, Chesapeake Bay Retrievers, Collies, Corgis, Irish Setters, Kerry Blue Terriers, Labrador Retrievers, Old English Sheepdogs, Rhodesian Ridgebacks, Siberian Huskies, Standard Poodles and Weimaraners.

The average age of onset is 9 years, and males are stricken more often than females. Since most dogs don't develop the disease until middle age, it's best to avoid breeding any dogs that have a family history of DM.

Sadly, there is no proven effective treatment for degenerative myelopathy, although some veterinarians believe that a regimen combining exercise, vitamin supplements and aminocaproic acid can help slow its progression. In most animals, however, their condition will deteriorate over six months to a year, to the point where the dog is unable to walk. At this point, most animals must be euthanized. However, there are steps an owner can take to make their pet more comfortable during its last months and help the animal adjust to its increasing limitations. These include placing carpeting down over slippery surfaces, walking the dog regularly and providing love and support whenever the animal appears fearful or confused. Be sure to stay in touch with your vet as well, since he or she may have other suggestions to make your dog more comfortable.