Vitamin D Status and Response to Supplementation as Predictive Factors for Early Remission in Polymyalgia Rheumatica: A Retrospective Longitudinal Investigation

<b>Background/Objectives:</b> Polymyalgia rheumatica (PMR) is a relatively common inflammatory rheumatic disease of the elderly. The role of vitamin D remains unclear in this condition. The endpoints of this study were to assess 25-hydroxyvitamin D [25(OH)D] serum concentrations in PMR patients with active disease compared to elderly controls and to determine if baseline levels or changes following supplementation [delta 25-hydroxyvitamin D, Δ25(OH)D] were associated with improved clinical outcomes. <b>Methods:</b> In this retrospective, case-control study, 29 PMR patients (55% males, 75.24 ± 9.6 years old, disease duration of 3.8 ± 3 months) were included, meeting the 2012 EULAR/ACR classification criteria, with 29 age- and sex-matched controls without systemic inflammatory rheumatic diseases. We assessed demographic, clinical and laboratory features for PMR patients, including baseline 25(OH)D serum concentrations, disease activity (polymyalgia rheumatica activity score), and serum inflammatory biomarkers. A subgroup of them (<i>n</i> = 25) was followed longitudinally, for an average period of 21.1 ± 17.7 months, to evaluate the association between Δ25(OH)D and clinical outcomes at follow-up using multivariate logistic regression. <b>Results:</b> Although lower than the normal reference values, baseline 25(OH)D concentrations did not differ significantly between PMR patients and controls (21.6 ± 9.2 vs. 22.7 ± 11.3 ng/mL, <i>p</i> = 0.66) and did not predict long-term clinical outcomes. However, after only 3 months of supplementation, the increase in 25(OH)D concentrations was significantly associated with a remission status, and patients in remission showed a significant increase in 25(OH)D compared to those with persistent disease activity (+22.02 vs. +1.33 ng/mL, respectively; <i>p</i> = 0.044). Notably, in the multivariate model, this Δ25(OH)D was the strongest independent predictor of remission (OR = 2.89; 95% CI [1.60-4.11]), an effect independent of prednisone dosage prescribed at first visit (<i>p</i> = 0.32) and glucocorticoid exposure at third month (<i>p</i> = 0.12). <b>Conclusions:</b> Individual's response of PMR patients to supplementation of vitamin D seems to be a robust independent predictor of early clinical remission achievement. Interestingly, optimizing vitamin D supplementation based on individual responsiveness may represent a valuable adjunctive strategy in PMR management.