Prevalence and incidence of type 2 diabetes mellitus in patients with adrenal incidentalomas: a study of 709 cases

Aim To evaluate the prevalence and incidence of type 2 diabetes in patients with nonfunctioning adrenal incidentalomas (NFAI) or adrenal incidentalomas (AI) with autonomous cortisol secretion (ACS). Methods In this single-center retrospective study, all patients with adrenal incidentalomas ≥1 cm and ACS or NFAI studied between 2013 and 2020 were included. ACS was defined by a post-dexamethasone suppression test (DST) serum cortisol concentration ≥1.8 μg/dl, in the absence of signs of hypercortisolism, and NFAI was defined as a DST < 1.8 μg/dl without biochemical evidence of hypersecretion of other hormones. Results Inclusion criteria were met by 231 patients with ACS and 478 with NFAI. At diagnosis, type 2 diabetes was present in 24.3% of patients. No differences were found in the prevalence of type 2 diabetes (27.7 vs. 22.6%, P = 0.137) between patients with ACS and NFAI. However, fasting plasma glucose values and glycated hemoglobin levels were significantly higher in patients with ACS than with NFAI (112 ± 35.6 vs. 105 ± 29 mg/dl, P = 0.004; and 6.5 ± 1.4 vs. 6.1 ± 0.9%, P = 0.005, respectively). Furthermore, patients with type 2 diabetes had higher urinary free cortisol (P = 0.039) and late-night salivary cortisol levels ( P = 0.010) than those without type 2 diabetes. After a median follow-up of 28 months, no differences were found in the incidence of type 2 diabetes between the groups (HR 1.17, 95% 0.52–2.64). Conclusion Type 2 diabetes was present in one fourth of our cohort. We found no differences in its prevalence or incidence between the groups. However, glycemic control might be worse among diabetic patients with ACS. Higher concentrations of urinary and salivary cortisol were found in patients with than without type 2 diabetes.