Hyperadrenocorticism better known as Cushings Disease is a relatively common disorder of middle aged to older dogs. The disorder is caused by an increase in the production of corticosteroids from the adrenal gland. The adrenal gland normally produces corticosteroids when the blood levels drop or when the body needs an increase in the level of steroids like in a fight or flight syndrome. The pituitary gland produces hormones that stimulate the adrenal gland to produce corticosteroids. If there is a tumor in the pituitary gland, it will produce steroids even when blood levels are adequate. If there is a tumor of the adrenal gland, it will produce steroids even if there are adequate levels in the blood, and no stimulation from the pituitary gland.
The resulting clinical signs are increased thirst and urination, increased appetite, and panting. Dogs that have Cushings disease tend to be overweight and have pendulous abdomens, have thin skin, and are predisposed to infections because steroids cause suppression of the immune system. Cushings disease also causes pulmonary hypertension which can lead to cardiac disease. High levels of systemic steroids also can lead to pancreatitis which can result in diabetes mellitus.
Clients that have diabetic pets that also have Cushings disease, have a difficult time controlling their pets’ insulin needs because Cushings can cause insulin resistance. The most common cause of Cushings disease in veterinary practice is iatrogenic. This means that we veterinarians and clients actually can cause the disease by overprescribing steroids for the treatment of skin allergies. Clients tend to want their dog to stop scratching yesterday, and steroids are quick and inexpensive. I try to discuss the causes of the allergies, ie food, fleas, inhalants and treat the cause rather than treating the symptoms. We try antihistamines, and omega 3 fatty acids first, and discuss flea control, and food trials before we resort to steroids.
We veterinarians, become suspicious of Cushings disease when we run blood panels and the alkaline phosphatase ( a specific liver enzyme) is elevated when all the other liver enzymes are normal or slightly elevated. The enzyme alkaline phosphatase is highly sensitive to steroids and is the first biochemical clue to early Cushings disease. This is one more reason we encourage routine annual blood panel screens for all pets. This way we can diagnose disease in the earliest and most treatable stage.
There are several tests to diagnose Cushings disease. There is a stimulation test and a suppression test. We do the stimulation test and send it to a lab in Tennessee that also measures hormone levels that are the precursors of corticosteroids. We have found this lab to be the most reliable one in diagnosing the disease.
There are several treatments for Cushings disease. Surgical treatment is impractical, very risky, and expensive. Medical treatment is aimed at management of the disease.