We have reported that a patient with painless thyroiditis induced by the cessation of dipeptidyl peptidase-4 inhibitor was accompanied with type 2 diabetes mellitus (T2DM). Given the lack of clarity regarding the possibility whether dipeptidyl peptidase-4 inhibitors (DPP-4is) attenuates thyroid hormone levels, we compared thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels between patients with T2DM who were not prescribed DPP-4is and patients with T2DM who were prescribed DPP-4is. 12 patients were prescribed DPP-4is (DPP-4is group) and 33 patients were not prescribed DPP-4is (w/o DPP-4is group). TSH and FT4 levels were measured in all of these patients and TSH and FT4 levels were annually measured in all of patients in the current population for more than three years. The TSH levels in the DPP-4is group was significantly higher than those of w/o DPP-4is group (2.11 ±0.67 vs1.58 ±0.64 μIU/mL, mean ±standard deviation, reference range: 0.33~4.05, p= 0.0189). The FT4 levels in the DPP-4is group was not significantly different from those of w/o DPP-4is group (1.06 ±0.086 vs1.01 ±0.12 ng/dL, mean ±standard deviation, reference range: 0.97~1.69, p= 0.0189). The measured TSH and FT4 levels were normal range in all of subjects in this clinical study. Nevertheless, TSH levels in patients with T2DM prescribed DPP-4is was significantly higher than those of the patients with T2DM not prescribed DPP-4is although we did not see the difference in FT4 levels between two groups. Despite of the small sample size, this clinical study provides important information. One strength of the current study is that the TSH and FT4 levels were annually measured in all patients with T2DM in the current population for more than three years. DPP-4is might modulate TSH levels in the absence of Metformin and further investigates with large population were necessary whether we need to monitor thyroid function regularly when we prescribe DPP-4is for the patients with T2DM.
Y. Shimoda: None. J. Okada: None. E. Yamada: None. T. Saito: None. S. Okada: None. M. Yamada: None.