The effect of Metformin treatment in obese insulin-resistant patients with euthyroid goiter

Objective The study’s objective was to evaluate the thyroid parameters in obese insulin-resistant patients with euthyroid diffuse or nodular goiter, following Metformin treatment. Patients and methods The study was experimental, open, and prospective. Fifty-three patients aged 18–68 were enrolled for two years. Obese insulin-resistant patients (cut-off Homeostasis-Model-Assessment of Insulin Resistance-HOMA-IR ≥ 2.5) with euthyroid nodular/diffuse goiter were included. Subjects with diabetes, hypo-/hyper-thyroidism, autoimmune thyroiditis, psychiatric disorders, liver or heart failure were excluded. Patients were randomly assigned to one of the following treatment: Metformin 1000 mg/day + Levothyroxine 25 μg/day (M + LT4 group) and only Levothyroxine 25 μg/day (LT4 group). Thyroid and metabolic parameters’ evolution was investigated over six months. Results The two groups were comparable at baseline (p ≥ 0.10). TSH, waist/hip ratio (WHR), visceral fat thickness (VFT), insulin, and HOMA-IR decreased significantly more in M + LT4 group compared to LT4 group. TSH decrease correlated with WHR reduction (p = 0.002) only in M + LT4 group. Moreover, the multivariate regression analysis revealed that insulin’s and HOMA-IR levels’ decrease was an independent factor associated with FT4’s increase (p = 0.031, p = 0.033) just in M + LT4 group. No other independent association between the evolution (Δ) of TSH, thyroid volume (TTV), thyroid nodules-maximum diameter (TN-MD), and metabolic parameters was found. In addition, no significant threshold between groups was reached when ΔFT4, ΔTTV, ΔTN-MD were compared (p > 0.07), although their significant improvement was recorded between the baseline and the follow-up moment in each group (p < 0.003). Conclusion Metformin added to obese insulin-resistant patients treated with Levothyroxine for diffuse/nodular goiter determined a significant decrease in TSH and metabolic parameters, compared to those treated with Levothyroxine alone, but no significant difference regarding thyroid morphology after 6 months.