Screening of Cushing's syndrome in adult patients with newly diagnosed diabetes mellitus

OBJECTIVE: Recent studies have shown that a relatively high number of diabetic patients may have unsuspected Cushing's syndrome (CS). The aim of the present study was to screen for CS in adult patients with newly diagnosed diabetes mellitus who were not selected for clinical characteristics, such as poor control and obesity, which may increase the pre-test probability of CS. DESIGN, PATIENTS AND MEASUREMENT: We prospectively evaluated 100 consecutive diabetic patients at diagnosis from 2003 to 2004. No patient had clear Cushingoid features. Screening was performed by using the overnight 1-mg dexamethasone suppression test (DST) after complete recovery from acute concomitant illnesses and attainment of satisfactory glycaemic control. The threshold of adequate suppression after DST was set at 110 nmol/l. RESULTS: Five patients failed to suppress cortisol after DST and underwent a repeated DST and a confirmatory standard 2-day, 2-mg DST after 3-6 months from the baseline evaluation. In one woman, a definitive diagnosis of CS was made by a surgically proven pituitary adenoma, and glycaemic control improved after cure of CS. CONCLUSIONS: The results of the present study support the view that unknown CS is not rare among patients with diabetes mellitus. This is the first demonstration that screening for CS may be feasible at the clinical onset of diabetes in an unselected cohort of patients. Therefore, early diagnosis and treatment of CS may provide the opportunity to improve the prognosis of diabetes.