Groups of related diseases are often combined into one category, for medical classification purposes. That's the case with polyneuropathy - an umbrella term that describes a group of disorders which affect multiple nerves. These diseases can strike any combination of nerves, and may be either inherited or developed later in the dog's life (acquired).
Polyneuropathy affects the peripheral nerves. These nerves are found outside of the brain and spinal cord, which together comprise the central nervous system. The term "neuropathy" simply means that some part of the peripheral nervous system isn't functioning properly.
Inherited polyneuropathy is the result of three chief causes. The first is spinal muscular atrophy, in which the muscles of the spine shrink and deteriorate. The second is demyelization, which causes destruction of the myelin, which is a protective sheath covering the nerves. Finally, the disorder can be caused by lysosomal storage diseases. The latter are inherited enzyme deficiencies that make the animal's body unable to perform normal metabolic functions.
In other cases, the disease is not inherited, but instead acquired later in life, caused by diabetes, hypothyroidism (hypoactive thyroid) or autoimmune disorders like lupus. Other conditions that cause inflammation of the muscles, joints and kidneys also can lead to polyneuropathy. Finally, an infectious organism known as neospora canis also can cause the problem.
Most of these disorders result in muscle weakness or paralysis, a loss in muscle tone and muscle mass, plus either reduced or absent muscle reflexes. Affected animals often have head tremors, seizures, and an unsteady gait. Some also lose their ability to feel pain, and may therefore injure themselves or make any existing injury worse without being aware of it. In severe cases, blindness can result, and the animal may become depressed and lethargic. Symptoms related to inherited neuropathy usually begin when the puppy is about six months old. They come on slowly and progress slowly over time. In acquired cases, the disease can appear in dogs of any age. The age of onset and how quickly symptoms develop depends upon the individual dog and the specific cause. Dogs with acquired neuropathy also may experience anorexia.
Any dog may be affected by polyneuropathy, and dogs with the inherited form of the condition should not be bred. The following breeds have the highest incidence of inherited polyneuropathy: Alaskan Malamutes, Boxers, Dalmatians, English Pointers, German Shepherds, Long-Haired Dachshunds, Rottweilers and Tibetan Mastiffs. For unknown reasons, Coonhounds have a higher rate of acquired neuropathy, even suffering from their own specific condition, known as coonhound paralysis.
A variety of blood, nerve, and muscle tests are used to diagnose polyneuropathy in dogs. Inherited forms of the disease are incurable, so treatment is focused on making the dog as comfortable as possible. Dogs with acquired neuropathy can be treated based upon the specific cause; immune-suppressing drugs like corticosteroids are often prescribed. When the animal is severely disabled or unable to walk, then nutrition, fluid, and electrolyte therapy also may be administered. Animals that cannot walk also must be treated and moved regularly to prevent the development of bedsores.