Adrenocorticotropin-independent bilateral macronodular adrenocortical hyperplasia: immunohistochemical studies of steroidogenic enzymes and post-operative course in two men.

We treated two men with Cushing's syndrome due to adrenocorticotropin (ACTH)-independent bilateral macronodular adrenocortical hyperplasia (AIMAH). In both patients, plasma ACTH was low and plasma cortisol was not suppressed by a high dose of dexamethasone (8 mg) but was remarkably responsive to exogenous ACTH. The adrenal glands were extremely enlarged and contained multiple nodules composed of large clear cells and small compact cells. The immunoreactivity of P-450(17) alpha was predominant in the small compact cells, while that of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) was observed exclusively in the large clear cells. Among various adrenocortical disorders, differential expression of 3 beta-HSD and P-450(17) alpha in clear and compact cells has heretofore been demonstrated only in AIMAH. Total adrenalectomy was done for one patient, and partial adrenalectomy for the other. In the former patient, the normal diurnal rhythm of plasma ACTH was restored 11 months postoperatively. In the latter patient, the normal dynamics in the hypothalamic-pituitary-adrenal axis became evident 15 months after surgery. Thus AIMAH is apparently a primary adrenocortical disorder and is not due to abnormalities of the hypothalamus or pituitary.