Background/Purpose: In cross-sectional studies it has been shown already that functional status in ankylosing spondylitis (AS), which represents probably the most important long-term outcome in this disease, is related to both the presence of structural damage in the spine and to disease activity. Nonetheless, studies investigating the clinical relevance of radiographic progression in the spine prospectively, especially early in the course of the disease, are lacking. The aim of the current study was to investigate the relationship between worsening of functional status, clinical disease parameters and radiographic spinal progression over two years in patients with axial spondyloarthritis (axSpA).

Methods: In total, 160 patients with early axSpA (91 with AS and symptom duration ≤10 years, and 69 with non-radiographic axSpA (nr-axSpA) and symptom duration ≤5 years) from the German Spondyloarthritis Inception Cohort (GESPIC) were included in the current analysis based on the availability of radiographic data and data on the functional status at baseline and after 2 years of follow-up. Spinal radiographs were scored according to the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) independently by two trained readers who were blinded for time point and all clinical data. Functional status was assessed by the Bath Ankylosing Spondylitis Functional Index (BASFI, 0-10 points), and clinical disease activity by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI, 0-10 points).

Results: In total, 44 patients (27.5%) of the patients demonstrated worsening of the BASFI by at least one point after 2 years as compared to baseline, and 20 patients (12%) experiences BASFI worsening in 2 points and more, which was considered to be clinically relevant. BASFI worsening by ≥1 point was significantly associated only with higher BASDAI worsening over 2 years in comparison to those without functional worsening: 1.2±1.4 vs -0.6±1.6, p<0.001. BASFI worsening by ≥2 points was, however, associated not only with increased disease activity (as reflected by BASDAI), but also with a higher rate of radiographic spinal progression - table. Importantly, in the multivariate analysis both BASDAI increase and progression of structural damage in the spine remained statistically significantly associated with BASFI worsening. No other disease-related parameters were found to be significantly associated with BASFI worsening over two years.

Conclusion: In this prospective study we could demonstrate that only 2 factors were significantly associated with worse functional outcome over two years in patients with early axSpA: 1) increase of disease activity (BASDAI) and 2) progression of structural damage. It seems that even a relatively small progression of structural damage such as an mSASSS worsening by 2 units or formation of a new syndesmophyte might have an impact on the functional status, even early in the course of the disease.