The relationship between metformin, thyroid function, and thyroid volume has been of interest to many investigators. A number of studies have consistently reported a TSH-lowering effect of metformin in hypothyroid patients. In addition, some previous reports found that metformin, alone or in combination with levothyroxine, shrank thyroid nodules in diabetic individuals with insulin resistance. Furthermore, other authors showed an anti-goitrogenic effect of metformin on subjects with type 2 diabetes (T2DM). Unfortunately, literature on the association between T2DM and thyroid volume is sparse.
We designed a two-group retrospective study with euthyroid T2DM patients treated with metformin (Group A) or with other anti-diabetes agents (Group B). Examined were basal TSH (mU/mL), HbA1c (%), BMI (kg/m2), and thyroid nodule size (mm) assessed by sonography. The same examinations were repeated one year later. Exclusion criteria included the following conditions: type 1 diabetes, thyroid dysfunction, levothyroxine or antithyroid treatment, and corticoid therapy. Results from Groups A and B were compared using the Student¿s t and the Mann-Whitney U tests.
A total of 63 nodules were analyzed. Group A included 31 nodules from 18 patients. Group B included 32 nodules from 15 patients. Groups A and B pre-TSH levels were 1.62± 1.19 and 2.06± 1.28, respectively; we found no statistically significant differences between them (p=0.164). Groups A and B post-TSH levels were 1.34± 0.87 and 1.99± 1.33, respectively; we observed a statistically significant difference between them (p=0.003). Groups A and B basal nodules mean size were 17.31± 9.97 and 12.45± 8.12, respectively. After one year of treatment, Groups A and B nodules mean size were 17.97± 10.31 and 12.90±7.92, respectively; we did not observe a statistically significant difference between them (p=0.961). We observed no statistically significant difference between Groups A and B in pre- and post-BMI, HbA1c, T2DM duration (data not shown). No patient in Group B was treated with glitazones.
Conclusions: Thyroid nodule size in euthyroid patients with T2DM diabetes remained unchanged following treatment with metformin for one year despite changes in TSH levels.
Nothing to Disclose: EP, GG, FG, BP, PA, JL, JE, JS, JCG
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