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

- Given patient has increased coisol & ACTH levels with cushingoid signs & symptoms. - This could result from either functional ACTH-secreting tumor in pituitary (Cushing's disease) or an ectopic tumor (such as a small cell carcinoma of lung, choice B). - To distinguish b/w these two,high doses of potent synthetic glucocoicoid(dexamethasone) is administered High-dose dexamethasone suppresses ACTH secretion at least by 50% in Cushing's disease Whereas secretion from ectopic tumor is not suppressed by dexamethasone. - As 75% suppression of coisol levels is seen in this pt, diagnosis is cushing's disease. OTHER OPTIONS: Addison's disease (choice A) is primary adrenal insufficiency, with increased plasma ACTH (producing hyperpigmentation) & decreased plasma coisol, aldosterone levels compared to normal. Conn's syndrome (choice C) results from hypersecretion of aldosterone by adrenal coex resulting in decreased ACTH production.