Longitudinal FIB-4 and APRI Monitoring in Psoriatic Arthritis: Associations with Cumulative Methotrexate Exposure and Biologic Therapy Class

Background: Psoriatic arthritis (PsA) is associated with hepatic risk, but longitudinal data during methotrexate (MTX) and biologic therapy are limited. We evaluated two-year changes in age-fixed FIB-4 and APRI and their associations with cumulative MTX exposure and biologic class. Methods: This retrospective cohort included 74 patients receiving continuous biologic therapy for 24 months. Baseline age was used to calculate FIB-4 at both time points. Logistic regression assessed factors associated with FIB-4 ≥ 1.3 at follow-up. Results: Forty-five patients received anti-TNF therapy and 29 received an IL-17 inhibitor. Age-fixed FIB-4 increased from 1.26 ± 0.44 to 1.72 ± 0.73 (p < 0.001); APRI did not change significantly (0.21 ± 0.08 to 0.23 ± 0.15; p = 0.155). No significant differences in either index were detected between biologic groups. Each 500-mg increase in documented cumulative MTX exposure was associated with higher odds of FIB-4 ≥ 1.3 (OR 2.164, 95% CI 1.04–4.41; p = 0.038). Conclusions: Greater documented cumulative MTX exposure was associated with FIB-4 ≥ 1.3 in an exploratory model. The findings neither establish a causal MTX effect nor demonstrate equivalence between biologic classes and require prospective validation against elastography or histology.