Cortisol secretion by an incidentally discovered nonfunctional adrenal adenoma

We describe a middle-aged man with late-onset multiple sclerosis and an incidentally discovered asymptomatic adrenal mass. He had no symptoms or signs of hypercortisolism. A 24-h profile revealed fluctuating serum cortisol values (between 15.1 and 4.7 micrograms/dl) and inappropriately low plasma ACTH values. Urinary cortisol excretion was 89 and 106 micrograms/day on two occasions. After a 4-h ACTH infusion, serum cortisol rose from 6.3 to 108 micrograms/dl. The serum dehydroepiandrosterone level, 33 ng/dl before ACTH stimulation, did not change. During dexamethasone administration, the lowest daily urinary cortisol excretion was 37 micrograms/day, and 17-ketosteroid excretion was 8 mg/day. The response to metyrapone showed a rise of serum 11-deoxycortisol to 25.6 micrograms/dl and of ACTH to 169.5 pg/ml. After removal of the tumor, most likely an adenoma, the circadian pattern of cortisol and ACTH was normal. During a 4-h ACTH infusion, the serum cortisol level rose from 10 to 27 micrograms/dl, and dehydroepiandrosterone rose from 62 to 90 ng/dl. During dexamethasone administration, daily urinary cortisol excretion decreased to 12 micrograms/day, and 17-ketosteroid excretion dropped to 3.9 mg/day. These data show that while the tumor appeared clinically to be nonfunctional, it was producing cortisol and possibly androgens autonomously, albeit at levels too low to cause complete suppression of the pituitary-adrenal axis.