Mendelian randomization was used to investigate the causal relationship between thyroid dysfunction (including hypothyroidism and hyperthyroidism) and carpal tunnel syndrome. Genetic loci independently associated with hypothyroidism and hyperthyroidism were selected as instrumental variables from pooled data from genome-wide association studies. Inverse variance weighting (IVW) was used to analyze the causal effect, supplemented by weighted median and MR-Egger. Heterogeneity test, pleiotropy testing and leave-one-out analysis were used to analyze the sensitivity test to explore the robustness of the results. Both hypothyroidism and hyperthyroidism increase the risk of carpal tunnel syndrome (hypothyroidism: IVW, OR = 1.04, 95% CI = 1.01-1.08, P = .017
hyperthyroidism: IVW, OR = 1.08, 95% CI = 1.05-1.12, P = 9.218E-06, no pleiotropy was found in both tests. Patients with thyroid dysfunction have an increased risk of carpal tunnel syndrome.