Comparative enthesitis burden in psoriatic arthritis vs axial spondyloarthritis: a cross-sectional analysis of the Swiss Clinical Quality Management in Rheumatic Diseases (SCQM) registry

Objectives This study aimed to compare prevalence, anatomical distribution, and associated factors of enthesitis in psoriatic arthritis (PsA) and axial spondyloarthritis (axSpA) in routine care. Methods Cross-sectional analysis of the Swiss Clinical Quality Management in Rheumatic Diseases (SCQM) registry. Patients with PsA or axSpA enrolled from 2018 to 2024 with an available Maastricht Ankylosing Spondylitis Enthesitis Score (MASES) recorded at first visit during study period were included. Enthesitis was defined as a MASES score of > 0. Axial PsA (axPsA) was analysed descriptively for anatomical distribution. Multivariable negative binomial regression modelled entheseal burden, adjusting for age, sex, body mass index (BMI), C-reactive protein levels, symptom duration, and current biologic or targeted synthetic disease-modifying antirheumatic drug use. Results We included 3885 patients (PsA, 1473; and axSpA, 2412). Enthesitis prevalence was 56.6% in PsA and 64.9% in axSpA. Among patients with any enthesitis, mean MASES score was 2.8 in PsA, 3.0 in axPsA, and 3.2 in axSpA. Posterior superior iliac spine and L5 spinous process were the most frequently affected sites. Achilles tendon involvement was more prominent in PsA and axPsA, whereas costochondral sites were more frequent in axSpA. Female sex, elevated C-reactive protein levels, higher BMI levels, and current smoking were consistently associated with higher enthesitis burden. Longer symptom duration and biologic disease-modifying antirheumatic drug use were associated with lower burden. No differential effects of BMI or smoking by diagnosis or sex were detected. Conclusions Enthesitis is common in PsA and axSpA, with distinct anatomical patterns but largely shared associated factors. Obesity, smoking, and systemic inflammation may represent relevant targets for intervention alongside pharmacologic management, though longitudinal studies are needed to confirm these associations.