A reappraisal of the ovine corticotropin-releasing hormone stimulation test in the differential diagnosis of cushing's syndrome: A comparison with the standard high-dose dexamethasone suppression test

Background. We evaluated the diagnostic efficacy of the ovine corticotropin-releasing hormone (oCRH) stimulation test in the differential diagnosis of Cushing's syndrome and compared it with the standard high-dose dexamethasone suppression test. Methods. Twelve healthy volunteers and 30 with Cushing's syndrome (12 Cushing's disease and 18 adrenal Cushing's syndrome) were enrolled. Plasma ACTH and cortisol levels were measured before and after an intravenous bolus of 100 μg oCRH. Plasma and urinary free cortisol were determined after standard 2-day high-dose dexamethasone suppression. Results. Basal cortisol in 12 patients with Cushing's disease and 18 with adrenal Cushing's syndrome were higher than the control group (21.4 ± 0.1 μg/dl vs. 22.3 ± 0.5 μg/dl vs. 9.1 ± 1.5 μg/dl; p