Early diagnosis of axial spondyloarthritis is associated with less long-term spinal structural damage: a longitudinal analysis of the Swiss Clinical Quality Management in rheumatic diseases registry.

OBJECTIVES: The Assessment of SpondyloArthritis international Society recently defined early axial spondyloarthritis (axSpA) as a duration ≤2 years of axial symptoms. Previous studies have shown no significant difference in short-term outcomes between early and established axSpA patients treated with biologic/targeted synthetic disease-modifying anti-rheumatic drugs. In order to evaluate long-term outcomes, we compared spinal radiographic progression between early and established axSpA patients followed under standard of care treatment in a large Swiss cohort. METHODS: Patients with axSpA who had at least two sets of spinal radiographs between 2004 and 2024 in the Swiss Clinical Quality Management registry were scored with the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) by two readers, and an adjudicator in case of disagreement. Longitudinal radiographic progression between early and established axSpA was compared (from the time of diagnosis) using a four-parametric logistic model, accounting for the non-linear progression of mSASSS. RESULTS: Among 376 patients with 1181 sets of radiographs, 138 patients had early and 238 had established axSpA. Baseline characteristics were similar between the two groups, with a male predominance (61%) and a high prevalence of Human Leukocyte Antigen (HLA)-B27 positivity (69%). Mean (SD) overall follow-up was 11.5 (8.6) years. Early axSpA patients exhibited a lower long-term mSASSS (-3.85 mSASSS units, 95%CI -7.28 to -0.42) compared to established axSpA. This difference became evident 10-15 years after diagnosis. The results remained statistically significant after adjustment for baseline radiographic damage (-5.70 mSASSS units, 95%CI -9.31 to -2.09). CONCLUSIONS: Early diagnosis is associated with lower long-term spinal structural damage.