Cushing's Disease, or hyperadrenocorticism, is caused by excessive cortisone production by the adrenal gland. The condition can occur in two different forms. Adrenal-dependent disease refers to a tumor on the adrenal gland that is producing excessive levels of cortisone. Pituitary-dependent disease refers to a tumor on the pituitary gland (the "master gland" located in the brain), which sends excess signals to the adrenal gland to produce cortisone. About 85% of dogs with Cushing's Disease have the pituitary form, while only 15% of affected dogs have the adrenal form. Cats can also develop this disease, with many of the same symptoms as dogs.
Cushing's Disease tends to occur in older dogs and cats — usually over 10 years of age. Common symptoms in dogs include "pot-bellied" appearance, symmetric hair loss over the trunk, thin skin, skin pigmentation, increased thirst and appetite, and increased urination. Cats show many of the same symptoms. The majority of cats with Cushing's Disease also have Diabetes Mellitus.
Cushing's Disease must always be viewed as a serious disease. Even with prompt diagnosis and treatment, serious complications are possible. Thromboembolism (blood clots), infection, hypertension, congestive heart failure, and central nervous system symptoms are all possible. The average lifespan after diagnosis — even with treatment — is about 2 years.
The doctor may suspect a diagnosis of Cushing's Disease based on history, physical examination, and routine blood tests; however, more specialized tests are required to confirm the disease. Diagnosis is sometimes rather straightforward, while at other times more difficult and frustrating. It is important to distinguish between pituitary-dependent disease and adrenal-dependent disease, since treatment sometimes varies. We also rely on ultrasound to help establish an accurate diagnosis.
Pituitary-dependent Cushing's Disease has traditionally been treated with a drug called Lysodren® in dogs. It is a compound that is toxic to the adrenal gland. An initial induction phase is typically given for 5-14 days, followed by lower dose maintenance therapy long-term. This is a potentially dangerous drug that needs to be monitored closely by the doctor. Several follow-up blood tests are necessary to ensure that the proper dosage is maintained.
We are increasingly treating canine Cushing's Disease with a newer drug called trilostane. It has a better safety profile compared to Lysodren and seems to control symptoms well in the majority of patients.
There are still no good drugs for use in cats. Several medications are currently being studied. Surgical removal of the adrenal glands is often the treatment of choice in cats.
Adrenal-dependent Cushing's Disease may be treated by surgical removal of the affected adrenal gland(s). Surgery can be risky, especially if the tumor has invaded large blood vessels nearby. Referral to a board-certified surgeon is warranted if surgical correction is being considered.