Cushing's syndrome, also called Cushing's disease, is an illness caused by the overproduction of a hormone called cortisol. It is most commonly caused by a defect or tumor of the pituitary gland, but in rarer cases, it is caused by a tumor of the adrenal gland.
Most dogs are at least 6 years old before they develop Cushing's, although it can occur in younger dogs. There are a variety of symptoms due to cortisol's effects on various bodily systems, and not all dogs exhibit all symptoms. Common ones include excessive drinking and urination, hair loss on the body but usually not the head or legs, increased appetite and a pot-bellied appearance. The dog may become lethargic and lose muscle mass as well. The immune system is often suppressed, leading to frequent infections.
Treatment varies depending on the cause. Pituitary-dependent Cushing's disease is treated with medications. The dog generally needs to take them for the rest of its life. Adrenal-dependent Cushing's is usually treated by removing the tumor or the entire cancerous adrenal gland. If this is not possible for some reason, medication may be used to control the symptoms, but this is generally less effective than medical treatment of the pituitary-dependent type. Most dogs with pituitary-dependent Cushing's have a good prognosis, while the prognosis for adrenal-dependent Cushing's depends on the cause of the tumor.