A 40-year old man with central obesity, "buffalo hump" and veical purple striae on abdomen, has fasting blood glucose levels in high normal range. Plasma levels of ACTH and coisol are both increased compared to normal. An overnight high-dose dexamethasone test produces 75% suppression of coisol levels. This patient most likely has
Addison's disease An ectopic ACTH-secreting tumor Conn's syndrome Cushing's disease