β-cell function and insulin sensitivity contributions on incident diabetes in patients with endogenous Cushing’s syndrome

Objective: To evaluate the relative contributions of beta-cell function and insulin sensitivity on the deterioration of glucose tolerance from OGTT in patients with endogenous CS. Methods: We retrospectively analyzed the data of 60 patients with CS and determined the glucose metabolism and beta-cell function through OGTT. Their general characteristics were retrieved. A series of parameters for assessing insulin sensitivity and beta-cell function was calculated. The logistic regression model was used to investigate insulin sensitivity and beta-cell function contributions on incident diabetes. Results: Of the 60 patients with CS, 10 (16.7%), 21 (35%), and 29 (48.3%) were classified as CS/ normal glucose tolerance (NGT), CS/prediabetes, and CS/diabetes mellitus (DM). Compared with the HCs, the CS/NGT patients had higher HOMA-IR and lower ISI-Matsuda but with a compensatory increase in HOMA-beta. Significant decreasing trends were observed in HOMA-beta, AUCI/ G and.I30/.G30 among CS/NGT, CS/prediabetes and CD/ DM groups. The OR of incident diabetes compared with the high AUCI/G/high ISI group was significant in the low AUCI/G/high ISI group. Conclusion: Impairment of the beta-cell function had a more profound effect on incident diabetes than decreased insulin sensitivity. An approach based on an OGTT has utility for diagnosing dysglycaemia and beta-cell dysfunction in patients with CS.