The changing states of fibromyalgia in patients with axial spondyloarthritis: results from the British Society of Rheumatology Biologics Register for Ankylosing Spondylitis

OBJECTIVES: To identify factors associated with FM development and recovery in patients with axial SpA (axSpA). METHODS: The British Society of Rheumatology Biologics Register for Ankylosing Spondylitis (BSRBR-AS) recruited patients with axSpA from 83 centres in a prospective study. FM was diagnosed using the self-reported Fibromyalgia Survey Diagnostic Criteria from 2015. Measures of axSpA disease activity and clinical findings were recorded at regular intervals. We identified predictors for FM development and recovery between yearly visits using uni- and multivariable logistic regression models. RESULTS: A total of 801 participants, 247 (30.8%) female, had two or more visits and were eligible for inclusion. A total of 686 participants did not have FM at baseline, of whom 45 had developed FM at follow-up, while 115 participants had FM at baseline, of whom 77 had recovered at follow-up. A high baseline BASDAI score [odds ratio (OR) 1.27 (95% CI 1.08, 1.49)] and Widespread Pain Index (WPI) [OR 1.14 (95% CI 1.02, 1.28)] were significantly associated with FM development in the final multivariable model. A low baseline BASFI score [OR 0.68 (95% CI 0.53, 0.86)] and WPI [OR 0.84 (95% CI 0.720, 0.97)] and starting a TNF inhibitor [OR 3.86 (95% CI 1.54, 9.71)] were significantly associated with FM recovery. CONCLUSION: High levels of disease activity and the presence of widespread pain is associated with the development of FM in patients with axSpA, while low levels of the same variables and starting a TNF inhibitor are associated with recovery from FM. The presence of comorbid FM should be considered in patients with persistent high axSpA disease activity and widespread pain.