Correlation between thyroid hormone sensitivity and diabetic peripheral neuropathy in euthyroid patients with type 2 diabetes mellitus

Previous studies have revealed that thyroid hormone (TH) levels are associated with the risk of diabetic peripheral neuropathy (DPN) in euthyroid patients with type 2 diabetes mellitus (T2DM). However, the relationship between TH sensitivity, a complementary method for assessing thyroid function, and DPN remains unclear. This study aimed to investigate the correlation between DPN and TH sensitivity in euthyroid patients with T2DM. Exactly 708 euthyroid adults with T2DM were retrospectively enrolled. The FT3/FT4 ratio was used to estimate peripheral TH sensitivity. Central TH sensitivity was assessed using the Thyrotroph T4 Resistance Index (TT4RI), Thyroid-Stimulating Hormone Index (TSHI), Thyroid Feedback Quantile-based Index (TFQI), and Parametric TFQI (PTFQI). DPN was assessed using neurologic symptoms, signs, and nerve conduction velocity tests. The relationship between DPN and TH sensitivity was examined using logistic regression analysis. We observed that an elevated FT3/FT4 ratio was associated with DPN (OR = 1.36, 95%CI: 1.13-1.63, p = 0.0012). For each standard deviation (SD) increase in the TT4RI, TSHI, TFQI, and PTFQI, the OR of DPN was 0.80 (95%CI: 0.68-0.94, p = 0.0078), 0.72 (95%CI: 0.60-0.86, p = 0.0002), 0.69 (95%CI: 0.58-0.83, p < 0.0001), and 0.69 (95%CI: 0.58-0.82, p < 0.0001), respectively. These results suggested that reduced central and peripheral TH sensitivity is associated with a decreased risk of developing DPN.