Sustained low functional impairment in axial spondyloarthritis (axSpA): which are the primary outcomes that should be targeted to achieve this?

OBJECTIVES: To (i) determine whether sustained disease activity states, as measured by Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score (ASDAS), impact function, and (ii) evaluate characteristics predicting sustained low functional impairment in a prospective axial spondyloarthritis (axSpA) cohort. METHODS: Biologic Treatment Registry Across Canada (BioTRAC) was a multi-center, prospective registry that collected real-world data on axSpA patients receiving infliximab or golimumab between 2006 and 2017. Generalized estimating equations (GEE) were used to test baseline characteristics, treatment, and duration (at 6 and 12 months vs. only at 6 or 12 months vs. neither) of low BASDAI (< 3), ASDAS-inactive disease (ID)(< 1.3), and ASDAS-low disease activity (LDA) in predicting sustained low Bath Ankylosing Spondylitis Functional Index (BASFI)(< 3) between 12 and 18 months. The adjusted impact of achieving low disease state at 6 and/or 12 months on BASFI at 18 months was analyzed by generalized linear models. RESULTS: Eight hundred ten patients were enrolled. 33.7%, 13.4%, and 24.7% achieved sustained low BASDAI, ASDAS-ID, and ASDAS-LDA, respectively. In univariable GEE of baseline variables, age and baseline BASDAI, BASFI, and ASDAS significantly predicted sustained low BASFI. In multivariable GEE, sustained low BASDAI (p < 0.001), low BASDAI only at 6 or 12 months (p = 0.001), and baseline BASFI (p < 0.001) were the only predictors of sustained low BASFI. Sustained ASDAS-ID (p = 0.040) and ASDAS-LDA (p < 0.001) were also predictors when forced into the model. Similar results were obtained when evaluating the BASFI score at 18 months. CONCLUSION: Sustained BASDAI < 3 may be a valid and feasible target for a treat-to-target strategy in axSpA having function as treatment goal. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13075-023-03055-1.