Long-Term Association Between Disease Activity and Disability in Early Axial Spondyloarthritis: Results From a Prospective Observational Study of Inflammatory Back Pain.

Abstract

Our primary objective was to study the long-term association between disease activity and disability in axial spondyloarthritis (SpA). Our secondary objective was to define patient profiles according to their level of disability. We analyzed data collected during the first 5 years of follow-up of a large early axial SpA cohort, the Devenir des Spondylarthropathies Indifferénciées Récentes (DESIR) cohort. Multivariable models were built to study the association between the Health Assessment Questionnaire for Ankylosing Spondylitis (HAQ-AS) and the Ankylosing Spondylitis Disease Activity Score with 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. Data from 644 patients and 5,152 visits were analyzed. HAQ-AS was longitudinally, independently, and positively associated with ASDAS-CRP (adjusted B [adjB] 0.205 [95% confidence interval (95% CI) 0.187, 0.222]), the enthesitis score (adjB 0.011 [95% CI 0.008, 0.015]), the Bath Ankylosing Spondylitis Metrology Index (adjB 0.087 [95% CI 0.069, 0.105]), and female sex (adjB 0.172 [95% CI 0.120, 0.225]). The CHAID decision tree revealed ASDAS-CRP as the first variable with discriminative power on HAQ-AS. The cutoffs that separated different patient disability profiles were obtained. 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 axial SpA. ASDAS-CRP cutoffs that separated different patient disability profiles largely mimicked the cutoffs previously defined for ASDAS-CRP disease activity states.