Evaluation of concomitant peripheral arthritis in early axial spondyloarthritis: results from a 24 month follow-up (Italian arm of SPACE study)

Objective: Although peripheral arthritis (PA) is common in early axial spondyloarthritis (axSpA), its influence on spinal/pelvic structural damage and disease activity remains unclear. We aimed to assess associations between PA, clinical and disease activity indices, and imaging features in early axSpA. Method: Baseline data analysis of the Italian SPACE cohort, including patients with chronic back pain (duration ≥3 months and ≤2 years; age of onset <45 years), was conducted. axSpA was diagnosed by magnetic resonance imaging and X-rays of the sacroiliac joints. Clinical features, disease activity, and functional indices were collected at baseline, and at 12 and 24 months. Characteristics of axSpA in patients with concomitant PA were evaluated over time using descriptive statistics. A logistic regression model was built to assess associations between baseline features and PA. Results: Ninety-one patients had axSpA (83.5% non-radiographic; 16.5% radiographic); 44% had PA. axSpA patients with PA less frequently had human leucocyte antigen B27 positivity (35% vs 43.1%; p = 0.02) and uveitis (5% vs 9.8%; p = 0.03) and more frequently had dactylitis (37.5% vs 0%; p < 0.01) and enthesitis (82.5% vs 56.9%; p = 0.02). Functional and disease activity indices improved overall. PA was independently associated with higher baseline C-reactive protein (p = 0.004) and dactylitis (p = 0.02) in multivariable analysis. Conclusion: axSpA patients with PA more often had other peripheral manifestations and increased disease activity and functional impairment, and revealed possible differences in axial involvement. These differences may be important in treatment decisions and warrant further investigation.