Cushing's Syndrome is a hormonal disease that primarily affects dogs. This condition results from the overproduction of the steroid cortisol. Steroids are produced in the adrenal glands that reside near the kidneys. The stimulus for the overproduction of cortisol is a benign tumor of the pituitary gland (80%) at the base of the brain or the adrenal gland (20%). The pituitary gland is a major hormone gland that signals several organs to produce other hormones or do a specific function. For the normal production of cortisol, the pituitary secretes the hormone ACTH that travels to the adrenal gland where cortisol is formed.
If there is a tumor on the pituitary gland, then an excess production of ACTH will occur which signals an increased production of cortisol. There are two adrenal glands that receive ACTH equally. Therefore, both glands will be enlarged.
If there is a tumor on one of the adrenal glands, then that gland will produce excess cortisol without need of direction from the pituitary gland. In this case, only the affected adrenal gland will be large. The other gland will be small or atrophied.
As a result of both tumor locations, the body has to deal with excessive steroids. In normal levels, steroids are vital. In excessive or minimal levels, the body can have significant side effects. The most common side effects of excessive steroids are excessive drinking and urination, pot-bellied appearance, thinning hair along the back/trunk, excessive appetite, enlarged liver, and continual panting.
Diagnosis begins with a detailed history and physical examination. Basic blood tests can point us in the direction of Cushing's disease but specific blood tests are required. The two most common tests for diagnosis is an ACTH stimulation test and a Low Dose Dexamethasone suppression (LDDS) test. The ACTH stimulation test is the most specific test that will accurately diagnose ("rule in") the disease in 8 of 10 patients. The LDDS test is more sensitive meaning that it can rule out the disease in over 9 of 10 patients. Your veterinarian will decide which test to run. On occasion, both tests may be performed. Depending on the results, it may be possible to not only diagnose Cushing's but also differentiate between pituitary dependent and adrenal dependent forms. An ultrasound of the abdomen can be performed to identify the size of the adrenal glands which may suggest one form of the disease over the other.
Treatment involves increasing the patient's quality of life. As the disease is a result of a tumor, medical management can only be supportive. Surgical options are available but rarely selected due to significant complications. Our goals of therapy are to decrease the clinical signs of excessive drinking and urination, increased appetite, pot-bellied appearance, and hair loss. Therapy is typically life long, and routine blood tests will need to be performed regularly.