Increased diagnostic probability of subclinical Cushing's syndrome in a population sample of overweight adult patients with type 2 diabetes mellitus.

Endogenous Cushing's Syndrome (CS) is unusual. Patients with subclinical CS (SCS) present altered cortisol dynamics without obvious manifestations. CS occurs in 2-3% of obese poorly controlled diabetics. We studied 103 overweight adult outpatients with type 2 diabetes to examine for cortisol abnormalities and SCS. All collected salivary cortisol at 23:00 h and salivary and serum cortisol after a 1 mg dexamethasone suppression test (DST). Patients whose results were in the upper quintile for each test (253 ng/dL, 47 ng/dL, and 1.8 microg/dL, respectively for the 23:00 h and post-DST saliva and serum cortisol) were re-investigated. Average values from the upper quintile group were 2.5-fold higher than in the remaining patients. After a confirmatory 2 mg x 2 day DST the investigation for CS was ended for 61 patients with all normal tests and 33 with only one (false) positive test. All 8 patients who had two abnormal tests had subsequent normal 24h-urinary cortisol, and 3 of them were likely to have SCS (abnormal cortisol tests and positive imaging). However, a final diagnosis could not to be confirmed by surgery or pathology. Although not confirmatory, the results of this study suggest that the prevalence of SCS is considerably higher in populations at risk than in the general population.