Prevalence and impact of suspected fibromyalgia on disease outcomes and treatment in axial spondyloarthritis: 10-year follow-up data from the DESIR cohort.

OBJECTIVES This study aimed to evaluate the prevalence of suspected fibromyalgia using the Fibromyalgia Rapid Screening Tool (FiRST) and its impact on disease burden, disability, TNF inhibitor (TNFi) initiation, and treatment retention over 10 years in patients with axial spondyloarthritis (axSpA) from the DESIR cohort. METHODS The FiRST questionnaire was administered annually from year 7 to year 10. Missing FiRST data were imputed using longitudinal multiple imputation. Patients were classified as suspected fibromyalgia-positive at baseline if they were FiRST-positive (FiRST ≥5/6) at least twice after multiple imputation. Associations with disease outcomes over the 10-year period were assessed using mixed models for repeated measures, adjusted for TNFi use. TNFi initiation and retention over 10 years were compared using Kaplan-Meier analyses. RESULTS The estimated prevalence of suspected fibromyalgia was 21.7% (144/663; 95% CI: 18.6-25.1). At baseline, suspected fibromyalgia was associated with a lower prevalence of HLA-B27 positivity and radiographic sacroiliitis, but similar rates of magnetic resonance imaging sacroiliitis and elevated C-reactive protein. Over 10 years, suspected fibromyalgia was consistently associated with higher self-reported disease activity, poorer health-related quality of life, and greater disability. Permanent disability at 10 years occurred more frequently in patients with suspected fibromyalgia (26.4% vs 9.4%; P < .001). TNFi initiation was more frequent (64.4% vs 46.1%), but treatment persistence at 1 year was significantly lower (42.0% vs 64.2%) in this group. CONCLUSIONS Suspected fibromyalgia is common and clinically relevant in axSpA. It is associated with higher disease burden, increased biologic use, and poorer treatment persistence.