Longitudinal Instability of Minimal Disease Activity Domains in Psoriatic Arthritis with Fluctuating Response: A Trajectory Analysis of a Real-World Cohort

Introduction: Minimal disease activity (MDA) is a composite tool used to measure disease state in psoriatic arthritis (PsA), but its longitudinal stability across individual domains remains insufficiently understood. We aimed to investigate domain-specific instability of MDA components over time in patients with fluctuating disease states. Methods: This post hoc analysis of a real-world longitudinal cohort included patients with PsA treated with biologic or targeted synthetic disease-modifying anti-rheumatic drugs (bDMARDs or tsDMARDs) who exhibited fluctuating trajectories over 24 months. MDA was assessed at 6-month intervals across seven domains. For each domain, an instability score (IS) was calculated as the number of transitions across the MDA cutoff between consecutive visits. Domains were also grouped into objective, tenderness-based, and subjective categories. Longitudinal instability patterns were analyzed and compared across domains. Results: Among 289 patients in the parent cohort, 107 (37.0%) exhibited fluctuating MDA trajectories and were included in the analysis. Objective domains showed the lowest instability over time, whereas tenderness-based and subjective domains demonstrated higher and more variable instability patterns. Domain-level analyses revealed marked heterogeneity across individual MDA components. Conclusions: In patients with PsA and fluctuating disease states, MDA instability is predominantly associated with subjective and tenderness-based domains, whereas objective inflammatory measures remain relatively stable. Domain-level analysis provides additional insight beyond composite MDA and may improve interpretation of longitudinal disease dynamics.