The desmopressin stimulation test in the differential diagnosis of Cushing's syndrome

objective We assessed the ability of desmopressin to stimulate the pituitary-adrenal axis in patients with Cushing's syndrome. DESIGN AND SUBJECTS The Cortisol response to 5 or 10 fig of intravenous desmopressin was evaluated in 31 patients with Cushing's syndrome of several aetiologies and in 15 normal subjects. RESULTS Cortisol responses were observed in 15 out of 16 patients with pituitary dependence and in two patients with adrenal nodular hyperplasia, the increase above baseline ranging from 61 to 379% in the responders. Eight patients with adrenal tumours and one with the ectopic ACTH syndrome did not respond to desmopressin, having shown changes In their Cortisol levels from -5 to 42% above baseline. Responses occurred in two out of the 15 normal Individuals, whose Cortisol increased 58 and 69% above baseline, respectively. Stimulation tests with standard agents as lysine vasopressin or ovine corticotrophin-releasing hormone were performed in the same patients and there was a high degree of concordance. No serious adverse reactions were observed in the tests with desmopressin. CONCLUSIONS Desmopressin was able to stimulate the pituitary-adrenal axis in patients with Cushing's disease and, like corticotrophin releasing hormone, it may prove useful in the differential diagnosis of Cushing's syndrome.