What causes Cushing’s syndrome (Hypercortisolism)?

What causes Cushing’s syndrome (Hypercortisolism)?

Too much cortisol causes Cushing’s syndrome. There may be many underlying causes of high cortisol levels, including:

• Use of glucocorticoid medications. Glucocorticoid medications (for example, prednisone) are used to treat many autoimmune diseases, for example chronic asthma, rheumatoid arthritis, lupus, sarcoidosis and many other diseases that result in chronic inflammation. Chronic treatment with these medications causes “iatrogenic” Cushing’s syndrome. Iatrogenic refers to something that is caused by a medical treatment.
• Pituitary tumors. Pituitary tumors that make too much ACTH (the hormone that tells the adrenal glands to make cortisol) cause eight out of 10 cases of Cushing's syndrome (excluding the cases of iatrogenic Cushing’s syndrome). This is called Cushing’s disease.
• Adrenal cortical tumors. A tumor on the adrenal gland itself can make too much cortisol. These are usually benign.
• Lung, pancreas, thyroid and thymus tumors. Tumors that develop outside of the pituitary gland can produce ACTH and this is called ectopic ACTH syndrome. These types of tumors are typically malignant. The most common type of these tumors is small cell lung cancer.