Cyclic Cushing's syndrome.

Cyclic Cushing's syndrome is a rare but increasingly recognized disorder of periodic fluctuations of adrenal steroid production. A case of cyclic Cushing's syndrome due to a pituitary adenoma is described. The patient demonstrated a prolonged cycle length of approximately six months, during which a spontaneous remission occurred both clinically and biochemically. Previously documented cases of cyclic Cushing's syndrome are reviewed, and the pitfalls in interpretation of results of dexamethasone suppression testing in the presence of spontaneous fluctuations in cortisol production are discussed.