In patients with axial spondyloarthritis (axSpA), comorbid fibromyalgia (FM) has only a modest effect on disease activity and QoL and does not significantly influence response to biological therapy, suggest data from the British Society for Rheumatology Biologics Register in Ankylosing Spondylitis (BSRBR-AS).
The BSRBR-AS study included 1757 participants with a physician diagnosis of axSpA, recruited from 83 secondary care centres across the United Kingdom. Just above 22% of participants met the 2011 criteria for FM.
Compared to those without FM at baseline, those who were FM-positive (FM+) at baseline had only modestly higher disease activity (Bath Ankylosing Spondylitis Disease Activity Index [BASDAI] difference 3.1; 95% CI, 2.8-3.3) and worse QoL (Ankylosing Spondylitis QoL [ASQoL] score difference 1.42; 95% CI, 0.88-1.96), after adjusting for demographic, clinical and lifestyle factors.
Poor QoL was more strongly determined by a high score on the Symptom Severity Scale (SSS) of FM criteria, indicating a high burden of somatic symptoms.
Persons who were FM+ had higher BASDAI scores on commencement of TNF-inhibitor therapy and throughout the 12-month follow-up. The difference in magnitude decreased during the treatment period.
FM status did not significantly influence the likelihood of meeting Assessment in SpondyloArthritis International Society (ASAS)20 or ASAS40 response criteria. Although FM status was not significantly related to treatment response assessed by BASDAI or ASQoL, high somatic symptom burden was associated with worse response.
The authors suggest it may be useful to identify patients with a high SSS who are commencing TNF-inhibitor therapy and to consider additional nonpharmacological therapies to target FM symptoms and potentially improve outcome.