Cyclical Cushing's disease: two distinct rhythms in a patient with a basophil adenoma.

A 71-yr-old woman with clinical signs of Cushing's syndrome was studied continuously for an extended period after demonstration of a paradoxical response to dexamethasone. She proved to have a corticotroph cell adenoma of the pituitary which caused secretion of ACTH and cortisol in two distinct rhythms. One rhythm consisted of a period of 40 days of excess cortisol production, followed by a period of 60-70 days of normal production. During the period of excess cortisol production there was a second rhythm, consisting of peaks of cortisol production every 3-6 days with intervening troughs of normal cortisol production. Prolonged clinical remission followed transphenoidal surgery, but the pituitary still has the ability to provoke abnormal amounts of cortisol secretion, as occurred during a postoperative dexamethasone suppression test. The long duration of normal cortisol production phases in this patient demonstrates the difficulty in excluding Cushing's syndrome in patients with suggestive clinical symptoms but normal serum and urinary cortisol levels if these tests are measured for a single short phase of several days.