Different sensitivity to adrenocorticotropin of dispersed adrenocortical cells from patients with Cushing's disease with macronodular and diffuse adrenal hyperplasia.

A patient with Cushing's syndrome and low plasma ACTH levels had a unilateral adrenal mass (diameter, 3 cm), which proved to consist of adenomatous hyperplasia. Dispersed adrenocortical cells prepared from this mass responded to ACTH with a maximal increment in cortisol release of more than 400%. Five months after operation Cushing's syndrome recurred. Computed tomography scanning showed an enlarged macronodular adrenal gland on the other side. The cells prepared from this adrenal gland were stimulated by ACTH by more than 600%. In adrenal glands from eight other patients with Cushing's disease cells from macroscopic nodules in hyperplastic adrenocortical tissue had increased responsiveness to ACTH in vitro, in comparison to cells from macroscopically diffuse hyperplastic adrenal tissue. The stimulability of the pituitary-adrenal axis (by metyrapone) and its suppressibility (by high dose dexamethasone) did not differ between the two groups of patients. These observations suggest that in the presence of adenomatous or macronodular adrenal hyperplasia lower circulating ACTH levels may sustain hypercortisolism than in diffuse adrenal hyperplasia. The presence of a unilateral adrenal mass and low normal plasma ACTH levels in patients with Cushing's syndrome, therefore, does not unequivocally indicate the presence of an autonomous adrenal adenoma. Tests with metyrapone and dexamethasone should still be carried out in order to make a secure differential diagnosis.