Who and how to screen for endogenous hypercortisolism in type 2 diabetes mellitus or obesity.

Purpose: The current review aims to summarize and discuss the prevalence of confirmed hypercortisolism in patients with diabetes mellitus or obesity, analysing the screening tests used and their accuracy, in order to better identify whether patients with diabetes mellitus and obesity should be screened for Cushing's syndrome (CS) and how.

Methods: A narrative review was performed including publications focusing on the current knowledge on prevalence of confirmed hypercortisolism in patients with type 2 diabetes mellitus (T2DM) or obesity and on screening tests used to detect CS.

Results: The studies reviewed suggest that the prevalence of CS in patients with T2DM is variable, ranging from 0.6 to 9.3%. The most used screening test is the overnight cortisol after 1 mg of dexamethasone suppression test (DST), with a false positive rate ranging from 3.7 to 21%. The prevalence of CS among obese patients is generally about 1%, except for two studies which reported higher prevalence. For obese patients, 1 mg DST and late-night salivary cortisol are the most accurate screening tests for CS.

Conclusions: Clinical expertise remains the mainstay to identify which subjects should be screened for CS. The evaluation of the clinical stigmata of CS and the combination with clinical comorbidities typical of CS are the stronger predictors of CS. In addition, we could hypothesize that in patients with T2DM, overnight 1 mg DST is the more accurate screening test for CS. By contrast, in patients with obesity both LNSC and overnight 1 mg DST could be equally used for the screening of hypercortisolism.