Vitamin D dynamics predict treatment response to intravenous glucocorticoids in thyroid-associated ophthalmopathy: a retrospective cohort study

Background: Intravenous glucocorticoids (IVGC) represent first-line therapy for active moderate-to-severe thyroid-associated ophthalmopathy (TAO). The relationship between vitamin D (VitD) and IVGC efficacy in TAO remains undefined. Methods: This retrospective study grouped TAO patients completing IVGC therapy with standardized VitD/calcium supplementation at First Affiliated Hospital of Xi'an Jiaotong University (2015-2019). Serum 25-hydroxyvitamin D (25(OH)D) and bone markers were measured pre/post-treatment. Multivariate regression and ROC analysis identified predictors. Results: In total, 52 TAO patients were enrolled, including 33 responders and 19 non-responders. Non-responders had significantly higher baseline triglycerides, thyroxine and longer duration of ophthalmopathy. Responders exhibited higher baseline β-CTX and N-MID OC. Notably, 73.08% of patients had baseline 25(OH)D deficiency (<20 ng/mL), with a significant 25(OH)D increase observed only in responders (P = 0.02). Between-group comparison showed that the treatment-induced change in 25(OH)D (Δ25(OH)D) was significantly greater in responders (P = 0.008), who also demonstrated larger improvements in clinical activity score (CAS), NOSPECS score, and diplopia. Multivariate analysis confirmed Δ25(OH)D as an independent predictor after adjustment for confounders (adjusted OR = 1.205, 95% CI:1.033-1.405; P = 0.017). ROC analysis showed Δ25(OH)D predicted response (AUC = 0.732, P = 0.006), with an optimal cutoff of +2.7 ng/mL. Predictive power was enhanced in males, patients ≥50 years, and baseline 25(OH)D -deficient subgroups. Conclusion: Δ25(OH)D is an independent predictor of IVGC response in TAO. Monitoring dynamic changes in serum 25(OH)D during therapy and targeting a minimum increase of 2.7 ng/mL may be associated with improved treatment outcomes, particularly in male, elderly, and VitD-deficient subpopulations.