Nodular adrenal hyperplasia with elevated adrenocorticotropic hormone levels.

Micronodular adrenal hyperplasia is an uncommon adrenal disorder characterized by failure of urinary corticosteroid excretion to be suppressed by high-dose dexamethasone therapy. Thus, micronodular adrenal hyperplasia demonstrates dexamethasone suppressibility that resembles primary adrenal neoplasia. However, since some cases have been reported to have measurable plasma adrenocorticotropic hormone (ACTH) levels, it is unclear whether this disorder arises primarily in the pituitary-hypothalamic region or in the adrenal gland. Our patient had clinical features of Cushing's syndrome and elevated urinary corticosteroid excretion that did not suppress with even high doses of dexamethasone; however, ACTH levels were elevated and were suppressible with high-dose dexamethasone therapy. At operation, enlarged adrenal glands with multiple micronodules were found. This case is compatible with the hypothesis that hypothalamic-pituitary hyperfunction precedes the development of micronodular adrenal disease in some cases.