Revealing the causal relationship between thyroidectomy, thyroid function status, and eczema: a bidirectional two-sample Mendelian Randomization study.

This Mendelian Randomization (MR) study aims to explore the potential bidirectional causal relationship between thyroidectomy, thyroid function status, and eczema. We utilized summary statistics from genome-wide association studies of European ancestry for thyroidectomy (4360 cases and 458,573 controls), hyperthyroidism (2547 cases and 334,612 controls), and hypothyroidism (337,199 samples), employing genetic instruments to investigate their association with eczema (461,199 samples), and vice versa. Primary causal estimates were obtained using the inverse variance weighting method (IVW), with a series of sensitivity analyses conducted to assess the robustness of the results. The study found that genetically predicted thyroidectomy has a negative effect on eczema (OR = 0.645; 95% CI 0.498-0.837; P < 0.001), while neither hyperthyroidism nor hypothyroidism showed significant causal associations with eczema. Reverse Mendelian Randomization analysis indicated that genetically predicted eczema does not significantly affect the incidence of thyroidectomy, hyperthyroidism, or hypothyroidism. To correct for the impact of post-thyroidectomy hypothyroidism on eczema, a multivariable Mendelian Randomization analysis was performed, treating thyroidectomy and hypothyroidism as exposures and eczema as the outcome. After adjusting for hypothyroidism, thyroidectomy still reduced the risk of developing eczema (OR = 0.632; 95% CI 0.476-0.838; P = 0.001). This study elucidates the bidirectional causal relationship between thyroidectomy, thyroid function status, and eczema, providing ancillary scientific evidence on the influence of thyroidectomy on the mechanism of eczema development.