Background 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, is related to both the presence of structural damage in the spine and to disease activity. However, studies investigating the clinical relevance of radiographic progression in the spine prospectively are lacking.

Objectives To investigate the relationship between worsening of functional status, clinical parameters and radiographic spinal progression over two years in patients with early 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 and symptom duration ≤5 years) from the German Spondyloarthritis Inception Cohort (GESPIC) were included in the current analysis based on the availability of clinical and radiographic data 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. Functional status was assessed by means of the Bath Ankylosing Spondylitis Functional Index (BASFI, 0-10 points).

Results In total, 44 patients (27.5%) of the patients demonstrated a worsening of the BASFI in at least 1 point after 2 years as compared to baseline, and 20 patients (12%) experiences BASFI worsening in 2 points and more. BASFI worsening in ≥1 point was significantly associated only with worsening of the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) 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 BASDAI change (1.5±1.6 vs -0.3±1.6, p<0.001), but also with a higher rate of radiographic spinal progression assessed by the proportion of patients with mSASSS worsening by ≥2 units (35.0% vs 13.6% in patients without BASFI worsening, p=0.024; odds ratio (OR)=3.4, 95%CI 1.2-9.7), with mSASSS worsening by ≥4 units (25.0% vs 5.7%, p=0.012, OR=5.5, 95%CI 1.6-19.0) or with new syndesmophyte formation (25.0% vs 6.4%, p=0.018, OR=4.9, 95% 1.4-16.4). On the level of absolute values, BASFI worsening by ≥1 points was associated with a mean mSASSS worsening of 1.3±4.0, and BASFI worsening by ≥2 points with mSASSS worsening of 2.6±5.6. Importantly, in the multivariate analysis both BASDAI increase and progression of structural damage in the spine remained significantly associated with BASFI worsening. There was a non-significant trend for the association of BASFI worsening with elevated acute phase reactants. No other disease-related parameters were found to be significantly associated with BASFI worsening over two years.

Conclusions 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.

Disclosure of Interest None Declared