Association Between Free Triiodothyronine and Diabetic Peripheral Neuropathy in Euthyroid Patients With Type 2 Diabetes.

Objective: To explore the relationship between free triiodothyronine (FT3) and diabetic peripheral neuropathy (DPN) in Euthyroid patients with type 2 diabetes mellitus.

Methods: We enrolled 1422 hospitalized patients with type 2 diabetes from Zhongshan Hospital, Fudan University. All participants underwent electromyographic examinations, including nerve conduction velocity (NCV), terminal motor and sensor latency (DML and DSL), sensory nerve action potential (SNAP) amplitude, and compound muscle action potential (CMAP) amplitude.

Results: A total of 519 (36.5%) patients with type 2 diabetes can be diagnosed as DPN according to their clinical symptoms and results of electromyography. Compared with those without DPN, the patients with DPN had a longer duration of diabetes, poorer blood glucose control and lower BMI levels, accompanied with higher proportions of diabetic retinopathy, diabetic nephropathy and cardiovascular disease (all p<0.05). Serum FT3 level were significantly lower in patients with DPN than those without DPN (4.08±0.64 vs 4.39±0.63 pmol/L, p<0.001), and FT3 was inversely correlated with the nerve DML and DSL, and positively correlated with the CMAP, SNAP, NCV of all nerves we measured in the patients with DPN (all P <0.05). The inverse correlation between serum FT3 and risk of DPN remained significant after multivariate adjustment for potential confounders (p<0.05). A mendelian randomization analysis also indicated a causal effect of serum FT3 on the risk of DPN.

Conclusion: Low FT3 is a risk factor of DPN among euthyroid patients with type 2 diabetes.