Cushing disease is caused by a tumor or excess growth (hyperplasia) of the pituitary gland. The pituitary gland is located at the base of the brain. A type of pituitary tumor called an adenoma is the most common cause. An adenoma is almost always benign (not a cancer).
With Cushing disease, the pituitary gland releases too much ACTH. ACTH stimulates production and release of cortisol, a stress hormone. Too much ACTH causes the adrenal glands to make too much cortisol.
Cortisol is normally released during stressful situations. It controls the body's use of carbohydrates, fats, and proteins and also helps reduce the immune system's response to swelling (inflammation).
Symptoms of Cushing disease include:
Upper body obesity (above the waist) and thin arms and legs
Stewart PM, Krone NP. The adrenal cortex. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, Pa: Elsevier Saunders; 2011: chap 15.
Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and /the A.D.A.M. Editorial team.