The aim of this study was to estimate insulin sensitivity (IS) in nondiabetic patients with adrenal incidentalomas (AI): nonfunctional adrenal incidentalomas (NAI) and patients with AI and subclinical Cushing's syndrome (SCS).
Based on the inclusion criteria (normal fasting glucose levels, no previous history of impaired fasting glucose and/or diabetes, and no medications or concomitant relevant diseases) and the exclusion criteria (pheochromocytoma, overt hypercortisolism, hyperaldosteronism, adrenal carcinoma, metastasis of extra-adrenal tumors, extra-adrenal malignancies), 142 subjects were drawn from a series of patients with AI. The subjects were age-, sex- and body mass index (BMI)-matched: 70 with NAI (50 women and 20 men), 37 with AI and SCS (31 women and 6 men) and 35 healthy control (HC) subjects (30 women and 5 men).
The oral glucose tolerance test (OGTT) and several indices of insulin sensitivity (IS) were used: homeostasis model assessment (HOMA), quantitative insulin sensitivity check index (QUICKI), triglycerides and glucose index (TyG), index of whole-body insulin sensitivity (ISI-composite) and glucose to insulin ratio (G/I).
There was a significant difference in IS between subjects with NAI and HC (HOMA, p=0.049; QUICKI, p=0.036; TyG, p=0.002; ISI-composite, p=0.024) and subjects with SCS and HC (AUC insulin, p=0.01; HOMA, p=0.003; QUICKI, p=0.042; TyG, p=0.008; ISI-composite, p=0.002). There was no difference in the tested indices of IS between subjects with NAI and SCS (p>0.05). However, subjects with SCS had a significantly higher prevalence of impaired glucose tolerance and higher area under the curve for glucose than subjects with NAI (p=0.0174). The linear regression analysis showed that 1 mg-DST cannot be used as a predictor of HOMA (R2=0.004, F=0.407, p=0.525). Significant relationship was found between 1 mg-DST and ISI-composite (R2=0.042, F=4.981, p=0.028) but this relationship was weak and standard error of estimate was high. The linear regression model also showed that ACTH cannot be used as a predictor of HOMA (R2=0.001, F=0.005, p=0.943) or ISI-composite (R2=0.015, F=1.819, p=0.187).
Insulin resistance is a major cardiovascular risk factor; therefore, the assessment of IS in patients with AI, even nonfunctional, has a valuable place in the endocrine workup of these patients.
Abbreviations:AI (adrenal incidentalomas), SCS (subclinical Cushing's syndrome), NAI (nonfunctional adrenal incidentaloma), HC (healthy control), IS (insulin sensitivity), IR (insulin resistance), HOMA (homeostasis model assessment), QUICKI (quantitative insulin sensitivity check index), G/I (glucose to insulin ratio), TyG (the product of triglycerides and glucose), ISI-composite (whole-body insulin sensitivity), OGTT (oral glucose tolerance test), ACTH (adrenocorticotrophic hormone), IGT (impaired glucose tolerance), IFG (impaired fasting glucose), 1mg-DST (overnight low dose dexamethasone suppression test), MSC (midnight serum cortisol), AUC (area under the curve), BMI (body mass index), CV (coefficient of variance)
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Published online: January 18, 2013
Accepted: December 9, 2012
Received: December 6, 2011
© 2013 Elsevier Inc. Published by Elsevier Inc. All rights reserved.