Metabolic syndrome and its components are associated with thyroid function, volume and nodule prevalence in euthyroid cases

The metabolic syndrome (MS) is a cluster of metabolic abnormalities with insulin resistance (IR) as a major characteristic. It has been recently questioned that MetS and its related components are associated with functional and morphological alterations of thyroid gland. Aim of our study is to examine thyroid volume and nodule prevalence in a case control study of patients with MS. Two hundred seventy eight patients with MS were randomly matched for age, gender,and smoking status with 261 subjects without MetS. Serum TSH, free T3 and T4, and the level of İR, estimated by the HOMA-IR, as well as other MS parameters were evaluated. Thyroid ultrasonography was performed in all participants. Thyroid nodules greater than 1cm underwent fine needle aspiration biopsy. TSH was significantly positively correlated with the presence of MS diagnosis. There was no association between free thyroid hormone levels and MS and its related components. Mean thyroid volume was higher in patients with MS than in controls (p<0.0001). Percentage of patients with thyroid nodules was also higher in patients with MS (50.4% vs. 14.6%, p<0.0001). Participants were also divided into two groups according to the presence of IR. Subjects with IR have also increased thyroid volume and nodule formation. The odds ratio for the development of thyroid nodule in the presence of IR was 3.2. TSH as well as all MS components were found to be independent risk factors for thyroid volume increase. IR but not TSH was found to be correlated with thyroid nodule formation. Thyroid cancer was diagnosed in 3/38 patients with MS (7.9%). No cancer cases were found in control subjects. The results suggest that patients with MS have significantly increased thyroid volume and nodule prevalence. In multivariate model, the presence of IR contributed substantially to this increased risk. Our data provide evidence that IR is an independent risk factor for nodule formation.