Preclinical Cushing's syndrome in patients with an adrenal incidentaloma

Autonomous (hyper-)secretion of cortisol without classical stigmata of Cushing's syndrome occurs in 10-15% of patients with incidentally detected adrenal tumors (incidentalomas).

We present the clinical and biochemical data of four such patients. Two patients had hypertension and one both hypertension and non-insulin-dependent diabetes mellitus, but none showed classical stigmata of Cushing's syndrome.

All patients showed insufficient suppression of plasma cortisol during a 1 mg dexamethasone screening test. Plasma ACTH levels were suppressed in all patients. However, in three out of four patients the diurnal rhythm of plasma cortisol was intact and these three patients also showed a response of plasma cortisol after administration of corticotropin-releasing hormone. All patients underwent unilateral adrenalectomy. A carcinoma was found in one patient and an adenoma in the remaining three. Postoperatively, blood pressure had normalized in 2 out of 3 hypertensive patients, whereas non-insulin-dependent diabetes mellitus had disappeared in 1 patient. Postoperative endocrine evaluation showed no abnormalities anymore.

We conclude that dexamethasone testing may reveal autonomous (hyper-)secretion of cortisol in adrenal incidentalomas. Adrenalectomy should be considered, especially when hypertension and/or non-insulin-dependent diabetes mellitus are present. One should be alert to the development of adrenal insufficiency after unilateral adrenalectomy.