Cushing's disease is an umbrella term that refers to a number of diseases that often occur when a person or dog is exposed to too much of a steroid hormone called glucocorticoids). Cushing's disease occurs when the body produces excessive amounts of steroid, usually because of a pituitary gland problem (e.g., a tumor or excessive growth), adrenal gland tumor, or too much steroid medication. In the great majority of cases (almost 80-85 per cent) the cause of excessive steroid production is a tumor of the pituitary gland in the brain.
Cushing's disease is extremely rare in cats, but it occurs with some regularity in dogs, especially middle-aged ones and those that weigh less than 20 kilograms. Breeds that are most likely to get Cushing's disease include poodles, terriers, beagles, boxers, and German shepherds. Cushing's disease progresses very slowly and initially very few owners notice that there is anything wrong with their pet. It sometimes takes from six months to six years before a diagnosis is made! This is primarily because changes occur so gradually at the outset that many owners think the changes are the result of normal aging.
The first and most common sign of Cushing's disease is often excessive thirst as well as excessive urination. Your dog may ask to be let out at night to urinate or may have accidents in the house. It may also have an increased appetite that leads to stealing food, eating garbage, and continuous begging at the table. This increased appetite may lead owners to believe that there is nothing really wrong with their pet. Other classical symptoms of Cushing's disease include abdominal enlargement (pot-bellied appearance), lethargy, panting, muscle weakness, and frequent skin infections. The Cushinoid dog often loses hair from the trunk of the body but not from the head or the legs. Diagnosis of this disease is usually via blood tests.
Treatment of Cushing's disease centers on decreasing or stopping the excessive production of steroids by the body. If the cause is a tumor, this could involve surgical excision of the tumor or of the adrenal gland. If this is not possible, drugs can be used, including mitotane ketoconazole, and more recently, 1-selegiline (Anipryl).
Anipryl is a new drug that was recently introduced for the treatment of Cushing's disease. Unlike mitotane, which destroys parts of the adrenal gland to keep it from producing too much steroid, 1-selegiline promotes normalization of the metabolism of a substance called dopamine. This results in a normal amount of steroid production and an amelioration of clinical signs.