Cushing's disease is a serious condition of an excess of the steroid hormone cortisol in the blood level caused by a pituitary tumor secreting adrenocorticotropic hormone (ACTH). ACTH is a hormone produced by the normal pituitary gland. ACTH stimulates the adrenal glands (located on top of the kidneys) to produce cortisol, commonly referred to as the stress hormone. Cushing's disease is rare, affecting 10 to 15 people per million each year, most commonly adults between 20 and 50 years of age. Women account for more than 70 percent of cases. Most patients with Cushing's disease have small tumors (pituitary microadenomas). Cushing's disease is not the same as Cushing's syndrome. Cushing's syndrome refers to the general state characterized by excessive levels of cortisol in the blood. Elevated cortisol level can occur for reasons other that a pituitary tumor such as tumors of the adrenal glands producing cortisol and certain types of ACTH producing cancer, elsewhere in the body (ectopic ACTH production). Cushing's syndrome is much more common than Cushing's disease. The most common cause of elevated cortisol level is taking medications that have cortisol, including hydrocortisone, prednisone pills, skin ointments, asthma inhalers and joint steroid injections. Less common causes of elevated cortisol levels are adrenal tumors and medical conditions such as depression, alcohol abuse, anorexia nervosa or high estrogen levels which may cause chronic elevation of cortisol levels ("Pseudo-Cushing's syndrome).
The symptoms related to Cushing's disease and Cushing's syndrome are the same, since both are related to an excess of cortisol. The symptoms may include different changes in physical characteristics of the body: fullness and rounding of the face (so-called "moon facies"), added fat on the back of neck (so-called "buffalo hump"), easy bruising of the skin, purplish stretch marks on the abdomen (abdominal striae), excessive weight gain (most marked in the abdominal region, while the legs and arms remain thin), red cheeks ("plethora"), excessive hair growth on the face, neck, chest, abdomen and thighs, generalized weakness and fatigue, menstrual disorders, decreased fertility and/or sex drive, high blood pressure, diabetes mellitus, mood and behavior disorders.
Regarding diagnosis, the early stages of Cushing's disease may be difficult to recognize, especially because the body changes develop slowly. In general, the first step in making the diagnosis is establishing a state of excessive blood cortisol (i.e. Cushing's syndrome). Assuming cortisol intake is excluded, this typically is done by hormone testing. After this diagnosis is established, an MRI is obtained to determine if a pituitary tumor is visible. If no tumor is visible, then inferior petrosal sinus sampling is indicated.