Use of the desmopressin test in the differential diagnosis of pseudo-Cushing state from Cushing's disease.

Context: The desmopressin (DDAVP) test has been proposed to discriminate Cushing's disease (CD) from pseudo-Cushing states (PC); however, current information on its value is scarce and contradictory.

Objective: The aim of the study was to assess the ability of the DDAVP test in distinguishing between these conditions, with emphasis on subjects with mild hypercortisolism.

Design And Setting: We conducted a retrospective/prospective study at the Division of Endocrinology, Polytechnic University of Marche, Ancona, Italy.

Patients: The study included 52 subjects with CD, 28 with PC, and 31 control subjects (CT).

Intervention(s): We performed the DDAVP test and standard diagnostic procedures for the diagnosis of Cushing's syndrome.

Main Outcome Measure(s): The diagnosis/exclusion of CD was measured.

Results: Interpretation of the DDAVP test based on percentage and absolute increment of cortisol and ACTH did not afford acceptable values of both sensitivity (SE) and specificity (SP). CD diagnosis based on simultaneous positivity for basal serum cortisol greater than 331 nmol/liter and absolute ACTH increment greater than 4 pmol/liter and its exclusion in subjects negative for one or both measures yielded an SE of 90.3% and an SP of 91.5%. The approach was also highly effective in distinguishing PC from: 1) CD with moderate values of urinary free cortisol (SE, 86.9%; SP, 92.8%); 2) CD with moderate values of serum cortisol after dexamethasone suppression (SE, 86.6%; SP, 92.8%); and 3) CD with moderate values of midnight serum cortisol (SE, 100%; SP, 92.8%).

Conclusions: Interpretation of the DDAVP test through a combination of parameters allowed effective discrimination of CD from PC, even in subjects with mild hypercortisolism.