High levels of disease activity and widespread pain in patients with axial spondyloarthritis (axSpA) are associated with development of fibromyalgia (FM), according to new research. Meanwhile, low levels of those variables and the initiation of a TNF inhibitor is associated with recovery from FM.

“The clinician should keep in mind that an unexpectedly high axSpA disease activity might have captured FM disease activity and that disentangling the two is necessary in order to target the therapy, while also considering the possibility of misdiagnosis,” wrote study authors led by Prof Sella A Provan, of Diakonhjemmet Hospital in Oslo and the University of Aberdeen.

The researchers retrospectively analysed data from 801 participants in the British Society for Rheumatology Biologics Register for Ankylosing Spondylitis; patients were included if they had attended at least two yearly follow-up visits. The results were published in Rheumatology.

At baseline, 686 of those patients did not have FM, while 115 patients did. Among those without FM at baseline, 45 patients developed it at follow-up visits, as assessed by the self-reported Fibromyalgia Survey Diagnostic Criteria.

A high baseline BASDAI score was significantly associated with development of FM, with an odds ratio of 1.27 (95% CI, 1.08-1.49; p < .05). The same was true for a high baseline score on the Widespread Pain Index, with an OR of 1.14 (95% CI, 1.02-1.28; p < .05).

Among the 115 patients with FM at baseline, 77 had recovered at follow-up. A low baseline BASFI score was associated with recovery from FM at follow-up, with an OR of 0.68 (95% CI, 0.53-0.86; p < .05), as was a low score on the pain index, with an OR of 0.84 (95% CI, 0.720-0.97; p < .05).

Starting a TNF inhibitor was also associated with recovery from FM, with an OR of 3.86 (95% CI, 1.54-9.71; p < .05).

The main take-home messages, according to senior author Gary J. Macfarlane, a professor of epidemiology and the dean of research at the University of Aberdeen, primarily regard an increased appreciation for the overlaps between the two conditions.

It’s about “awareness that fibromyalgia is a common comorbidity of axSpA, it is most likely to develop in the context of high disease activity, but the state is not usually permanent,” he told the limbic.