Background/Purpose: Some patients with axial spondyloarthritis (axSpA) are recognized clinically to have co-morbid fibromyalgia (FM). However, there are no trials to inform how these patients are best managed when axSpA and FM occur together. This study aims to provide data on their frequency of co-occurrence and, amongst persons with axSpA, features which characterize persons with co-morbid FM

Methods: The British Society for Rheumatology Biologics Register in Ankylosing Spondylitis (BSRBR-AS) recruits persons meeting any ASAS definition of axSpA. All patients recruited are naïve to biologic therapy and are either newly starting biologic therapy (biologic cohort) or not (non-biologic cohort). At recruitment, patients self-complete the ACR 2010 modified research criteria (2010m ACR) for FM, Bath measures of disease activity (BASDAI), function (BASFI) and global severity (BAS-G), Quality of Life (ASQoL and EQ-5D), sleep disturbance score (SDS), Chalder Fatigue Scale (CFS), and Hospital Anxiety and Depression Scale (HADS). Clinicians indicated whether they had made a clinical diagnosis of FM; Bath metrology index (BASMI) and Body Mass Index (BMI) were measured. The Index of Multiple Deprivation (IMD) is an area based measure of deprivation based on postcode.

Results: 430 patients provided clinical information and the recruting clinicians considered that 13 had a clinical diagnosis of FM (3.0%), while 274 provided self-report data, of whom 56 (20.4%) met the 2010m ACR FM criteria. Patients who met FM criteria were more likely to be female (difference in proportion 0.21; 95% CI (0.07, 0.36), reported worse BASDAI (mean difference (md) 2.7; 95% CI 2.0, 3.3), BASFI (md 2.7; 1.9, 3.4) and BAS-G (md 2.7; 2.0, 3.5). They reported worse Quality of Life (ASQoL md 6.3; 4.8, 7.8: EQ-5D md -0.23; -0.32,-0.14), higher levels of anxiety (md 3.9; 2.7, 5.1) and depression (md 4.0; 2.9, 5.2), more sleep problems (md 3.7; 2.0, 5.4) and higher levels of fatigue (md 4.0; 3.0, 5.0). There was no difference in age, IMD or whether they were commencing biologic therapy.

Conclusion: There is a large discrepancy between clinical diagnosis of FM and meeting FM research criteria in patients with axSpA. Patients who meet FM criteria show markedly worse markers of axSpA disease activity and generally poorer health. It is unknown whether such criteria are valid in the presence of axSpA, but there may be a large unmet and unrecognised need for treatment of FM symptoms amongst patients with axSpA.  

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-co-occurrence-of-axial-spondyloarthritis-and-fibromyalgia-a-national-register-based-study/