Longitudinal association of early axial spondyloarthritis status at the time of diagnosis with disease activity over time

\(\bf Objective\) Recently, the definition for "early axial spondyloarthritis (axSpA)" was developed by the Assessment of SpondyloArthritis international Society (ASAS), including \(\leq\)2 years of axial symptoms as a key element. The aim of this study was to analyse the longitudinal association of early axSpA with achieving low disease activity or inactive disease. \(\bf Methods\) Using 10-year longitudinal data from the German Spondyloarthritis Inception Cohort (GESPIC), a generalised estimating equations model was fitted to estimate the effect of early axSpA on disease activity, as measured by the Axial Spondyloarthritis Disease Activity Score (ASDAS). The model adjusted for confounders identified through a directed acyclic graph and accounted for repeated measurements within patients. Additional analyses were conducted, including stratification by radiographic status (non-radiographic — nr or radiographic — r). \(\bf Results\) Of 525 patients (277 nr-axSpA, 248 r-axSpA) included in GESPIC, 161 (30%) fulfilled the ASAS early axSpA consensus definition (115 nr-axSpA and 46 r-axSpA) at baseline. Over the 10-year follow-up period, patients with early axSpA consistently achieved ASDAS states of inactive disease or low disease activity at a higher rate than those with non-early axSpA, rising from 41% versus 30% at baseline to 57% versus 44% at year 10. The total effect of early axSpA on ASDAS was −0.42 (95% CI: −0.57 to –0.26). Stratification by r-axSpA/nr-axSpA showed a total effect of −0.50 (95% CI: −0.81 to –0.19) for r-axSpA and −0.28 (95% CI: −0.46 to –0.10) for nr-axSpA. \(\bf Conclusion\) Fulfilment of the ASAS early axSpA definition at inclusion was associated with lower disease activity over 10 years.