The desmopressin test in the differential diagnosis between Cushing's disease and pseudo-Cushing states

Differentiating Gushing's disease (CD) from pseudo-Gushing (PC) states may still be difficult in current practice. Because desmopressin (1-deamino-8D- arginine vasopressin, DDAVP), a vasopressin analogue, stimulates ACTH relea se in patients with CD but not in the majority of normal, obese, and depres sed subjects, we investigated its ability to discriminate CD from PC states ; One hundred seventy-three subjects (76 with active CD, 30 with PC, 36 wit h simple obesity, and 31 healthy volunteers) were tested with an iv bolus o f 10 mu g DDAVP. Sixty-one of these subjects also underwent a control study with saline. DDAVP induced marked ACTH and cortisol rises in CD (P < 0.005 us. saline, for both ACTH and cortisol) but not in PC. A significant ACTH elevation occurred upon DDAVP administration also in normal and obese subje cts, but it was much smaller than that observed in patients with CD (P < 0. 0001). A peak absolute ACTH increase (greater than or equal to 6 pmol/L), a fter DDAVP, allowed us to recognize 66 of 76 patients with CD and 88 of 97 subjects of the other groups. The same criterion correctly identified 18 of 20 patients with mild CD (24-h urinary free cortisol less than or equal to 690 nmol/day) and 29 of 30 PC, resulting in a diagnostic accuracy of 94%, which was definitely higher than that displayed by urinary free cortisol, o vernight l-mg dexamethasone suppression test, and midnight plasma cortisol. In conclusion, the DDAVP test seems to he a useful adjunctive tool for the evaluation of hypercortisolemic patients chiefly because of its ability to differentiate mild CD from PC states.