Cushing's disease is due to an ACTH-secreting pituitary adenoma. ACTH-dependent Cushing's syndrome can also be caused by an ectopic ACTH producing tumor. Excessive secreted amounts of corticotropin-releasing hormone by an ectopic tumor are a rare cause of Cushing's syndrome. The excess of ACTH results in overproduction of glucocorticoids and to a much lesser extent of mineralocorticoids and androgens.
Increased glucocorticoid levels result in the characteristic symptoms such as moon face, myopathy, obesity, buffalo hump, hypertension, and glucose intolerance. A pituitary adenoma can be removed by transsphenoidal microsurgery. Preoperative pharmacological treatment is focused on the inhibition of glucocorticoid synthesis in the adrenals.
I. Obesity is often caused by Cushing’s disease.
II. The first diagnostic step for pathological overproduction of cortisol in Cushing’s syndrome or disease is based on decreased suppression of plasma cortisol after dexamethason and increased free cortisol in 24h urine.
Extra info: Obesity is only rarely caused by Cushing’s disease. The 1 mg dexamethason suppression test is the initial test to diagnose pathological overproduction of cortisol. In addition, the excretion of free cortisol in 24h urine collection is used as a second diagnostic test.