Objectives: Our primary objective was to study the long-term association between disease activity and disability in axial spondyloarthritis (axSpA). Our secondary objective was to define patient profiles according to their level of disability.
Methods: We analysed data collected during the first five years of follow-up of a large early axSpA cohort - the Devenir des Spondylarthropathies Indifferénciées Récentes (DESIR) cohort. Multivariable models were built to study the association between Ankylosing Spondylitis Health Assessment Questionnaire (HAQ-AS) and Ankylosing Spondylitis Disease Activity Score C-reactive protein (ASDAS-CRP), adjusting for potential confounders. Hierarchical multivariable analysis was conducted using the Chi-square Automatic Interaction Detector (CHAID) method, to help determine how variables best cluster to explain HAQ-AS.
Results: Data from 644 patients and 5152 visits were analysed. HAQ-AS was longitudinally, independently and positively associated with ASDAS-CRP [adjusted (adj) B=0.205, (95% confidence interval (CI)= 0.187 to 0.222], enthesitis score (adjB=0.011, CI=0.008 to 0.015), Bath Ankylosing Spondylitis Metrology Index (BASMI) (adjB=0.087, CI=0.069 to 0.105) and female gender (adjB=0.172, CI=0.120 to 0.225). The CHAID decision tree revealed ASDAS-CRP as the first variable with discriminative power on HAQ-AS. The cut-offs that separated different patient disability profiles were obtained.
Conclusion: Disease activity contributes longitudinally to disability and is hierarchically superior to any other variable in explaining this health domain. Enthesitis and spinal mobility are also key drivers of disability in early axSpA. ASDAS-CRP cut-offs that separated different patient disability profiles largely mimicked the cut-offs previously defined for ASDAS-CRP disease activity states.
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