Pituitary Carcinoma Mimics the Ectopic Adrenocorticotropin Syndrome

Abstract

A middle-aged man presented with weight loss, hypokalemic alkalosis, diabetes, hypertension, and generalized melanosis. Marked elevation of urinary free cortisol (655 µg/24 h) and plasma ACTH (2445 pg/ml) suggested the diagnosis of ectopic ACTH syndrome. The plasma concentrations of cortisol and urinary 17-hydroxycorticosteroids increased paradoxically during the administration of dexamethasone without a corresponding change in the plasma ACTH level. Metyrapone administered over 24 h also markedly increased both urinary free cortisol and 17-hydroxycorticosteroids. Selective venous sampling of plasma ACTH did not reveal a gradient between jugular vein and peripheral venous blood. The laboratory findings supported the diagnosis of ectopic ACTH syndrome. However, belated occurrence of visual changes necessitated surgical exploration, resulting in the diagnosis of pituitary carcinoma. A fluorescent antibody to ACTH reacted strongly withthe atypical pituitary cells. This rare case documents that severe melanosis in Cushing’.s disease can occur without prior adrenalectomy and is consistent with the diagnosis of pituitary carcinoma. Furthermore, melanosis observed in patients with pituitary carcinoma is associated with ACTH levels similar to those occurring in the ectopio ACTH or Nelson’s syndrome.