Co-Occurrence and Characteristics of Patients With Axial Spondyloarthritis Who Meet Criteria for Fibromyalgia: Results From a UK National Register

Objective: To estimate the proportion of patients with axial spondyloarthritis (axSpA) who meet criteria for fibromyalgia (FM) and to characterise such patients.
Methods: The British Society for Rheumatology Biologics Register of Ankylosing Spondylitis (BSRBR-AS) recruits two cohorts of patients who meet ASAS criteria for axSpA across 83 centres in the United Kingdom. Patients are either newly starting (biologic cohort) or naïve (non-biologic cohort) to biologic therapy and are followed prospectively. At recruitment and follow-up, clinical information and measurements are recorded, while patients complete the 2011 research criteria for FM, assessments of disease activity and impact.
Results: 1504 patients (68% male) were eligible for the current analysis of whom 311 (20.7%) met criteria for FM. Prevalence was similar among those who fulfilled modified New York (mNY) criteria (19.7%), and ASAS imaging but not mNY criteria (25.2%), but lower among those who only fulfilled ASAS clinical criteria (9.5%). Patients who met FM criteria reported significantly worse disease activity, function, global severity scores, quality of life and were more likely to have moderate/severe levels of mood disorder and clinically important fatigue. They reported work impairment around half the time. Meeting FM criteria was not related to elevated C-reactive protein, or most extra-spinal manifestations, but was associated with a higher likelihood of having received biologic therapy.
Conclusion: Developing management approaches that address the significant unmet needs of the 1 in 5 axSpA patients who meet criteria for FM should be a research priority.