Adrenocorticotropic hormone-independent bilateral adrenocortical macronodular hyperplasia as a distinct subtype of Cushing's syndrome. Enzyme histochemical and ultrastructural study of four cases with a review of the literature.

Four patients with adrenocorticotropic hormone (ACTH)-independent bilateral adrenocortical macronodular hyperplasia (AIMAH) were examined. All of them were men whose ages ranged from 37 to 52 years. Plasma cortisol levels were high, with a loss of diurnal rhythmicity, and plasma ACTH was undetectable. Adrenal cortisol secretion was not suppressed by dexamethasone, but it was ACTH responsive. Test results for corticotropin-releasing hormone (CRH) also were negative. Image analyses revealed a normal sella turcica and significantly enlarged adrenal glands, which showed enhanced uptake of isotope. Both adrenal glands in all cases were between 72 and 176 g in combined weight and were composed of, and distorted by, yellow nodules. Histologically, small cortical cells with or without lipid, occasional clear cells, and rare compact cells of the usual size were increased in number in the glandular cords. Enzyme histochemically, cortical cells showed weaker activity for 3 beta hydroxysteroid dehydrogenase and other enzymes than did usual cortisol-producing adenomas. Ultrastructurally, they had moderately to poorly developed smooth endoplasmic reticulum. Nonnodular areas of the cortex consisting of nonproliferating cells were atrophic and contained no compact cell zone. This is similar to the adrenal cortices attached to cortisol-producing adenomas. These features are unique to AIMAH and suggest the presence of a distinct subtype of Cushing's syndrome.