Relationship between thyroid nodules and non-functioning adrenal incidentalomas and their association with insulin resistance.

OBJECTIVE: The relationship between insulin resistance and thyroid nodules in patients with non-functional adrenal incidentalomas (AI) is not clearly understood. The aim of this study was to determine the frequency of thyroid nodules in AI patients, as well as to evaluate any possible associations with disorders of insulin resistance. METHODS: Patients diagnosed with a non-functional AI were approached for inclusion in the study. Insulin resistance was evaluated using homeostasis model assessment (HOMA-IR). All participants were screened for the presence of thyroid nodule by ultrasonography, and fine needle aspiration biopsies were obtained from consenting subjects. RESULTS: One-hundred-thirteen patients with AI and 152 age-, BMI- and gender-matched healthy controls were enrolled. AI patients had higher waist circumference and waist/hip ratio than the control group. Metabolic syndrome, hypertension and type 2 diabetes mellitus rates were significantly higher in AI patients. HOMA-IR was similar between the groups. At least one thyroid nodule was observed in 42 (27.6%) of the controls compared to 55 (48.7%) of AI patients (p < 0.001). The mean number of thyroid nodules in AI patients was significantly higher than the control subjects (2.4 ± 0.9 versus 1.7 ± 1.0, p = 0.008). Mean nodule volume was similar between AI patients and the controls. A correlation could not be established between adrenal tumor/thyroid nodule volumes and the number of thyroid nodules, HOMA-IR, waist circumference, waist/hip ratio, BMI and thyroid function tests. CONCLUSION: A higher prevalence of thyroid nodule and a higher number of thyroid nodules were determined in patients with AI compared to healthy controls.