Background/Purpose: It has been shown in the past that radiographic spinal progression is an important determinant of the functional outcome in patients with advanced axial spondyloarthritis (SpA). The objective of the current study was to investigate functional relevance of structural damage development in the spine in patients with early (up to 10 years symptom duration) axial SpA.

Methods: Altogether 210 patients with early axial SpA from the German Spondyloarthritis Inception Cohort (GESPIC) were included. Clinical data reflecting disease activity (BASDAI), functional status (BASFI), and spinal mobility (BASMI) were collected at baseline and every 6 months thereafter. Structural damage in the spine was assessed on spinal radiographs at baseline and after two years according to the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS).

Results: The association between the mSASSS and BASFI status scores at baseline was rather weak: the BASDAI-adjusted parameter estimate (b) in the linear regression analysis was 0.04 (95%CI 0.02-0.07). At the same time, BASDAI itself was strongly associated with BASFI at baseline: b=0.87 (95%CI 0.78-0.96). For the mSASSS change score after 2 years, the parameter estimate b was 0.04 (95%CI -0.05-0.21), meaning that radiographic progression in 25 mSASSS points over 2 years would be responsible for a 1-point difference in BASFI (adjusted for the BASDAI change and mSASSS at baseline). The cumulative probability plot (figure) also shows a week association between mSASSS change and BASFI change values. Similar results were obtained for the association between mSASSS and BASMI: b=0.09 (95%CI 0.07-0.12) for the status scores and b=0.01 (95%CI -0.08-0.09) for the change scores. Results of the linear regression analysis were confirmed in the mixed model analysis: the BASDAI-adjusted parameter estimates for the association between mSASSS and BASFI / BASMI were 0.06 (95%CI 0.04-0.08) and 0.08 (95%CI 0.05-0.11), respectively. In contrast, BASDAI change score demonstrated a strong association with the BASFI change score: b=0.61 (95%CI 0.50-0.71); association with the BASMI change score was weaker: b=0.16 (95%CI 0.05-0.26).

Conclusion: The functional relevance of the structural damage development in the spine in the majority of patients with early axial SpA seems to be low, while disease activity has a major impact on the function of the spine and should be, therefore, considered as the primary treatment target in these patients.