The concomitant presence of both axial spondyloarthritis (axSpA) and fibromyalgia affects response to tumor necrosis factor (TNF) blockers through increased symptom severity on patient-reported outcomes but not on more objective measurements, according to findings from a prospective, longitudinal study.

The results illustrate the importance of determining whether a patient has both conditions so that realistic and feasible treatment targets can be met, said the study authors, led by first author Anna Moltó, MD , of the Cochin Hospital in Paris.

Although reports have less frequently examined the relationship between fibromyalgia diagnosis and disease activity in patients who have rheumatologist-diagnosed axSpA than they have in patients with rheumatoid arthritis, those reports have indicated that patients with axSpA and concomitant fibromyalgia tend to present with higher disease activity on measures such as the Bath Ankylosing Spondylitis Disease Activity Index ( BASDAI ), the investigators wrote in Annals of the Rheumatic Diseases .

In this prospective, longitudinal study, a total of 508 adult patients with axSpA from 65 centers first attended a baseline visit, then 12 weeks after commencing treatment with TNF blockers, they attended an “effectiveness visit” in which they were evaluated for a response on the BASDAI. This response was defined as a reduction of at least 50% or two units, compared with baseline measurements. Furthermore, a total of 37.8% tested positive at baseline on the self-reported Fibromyalgia Rapid Screening Tool ( FiRST ) questionnaire, defined as a score of 5 or 6 out of 6.

These patients testing positive on FiRST at baseline were more likely to be female (55.7% vs. 41.1%), to have a history of peripheral enthesitis (64.7% vs. 47.8%), and to have a higher disease severity at baseline on the BASDAI and Ankylosing Spondylitis Disease Activity Score at baseline (6.5 vs. 5.1 and 3.5 vs. 3.2, respectively). They were also were more likely to be taking antidepressants (26.8% vs. 16.2%).

Patients who had fibromyalgia according to FiRST presented less frequently with a BASDAI response (87 of 192; 45.3%) after 12 weeks, compared with patients who had only axSpA at baseline (171 of 316; 54.1%). But this difference did not reach statistical significance in both univariate or multivariate analyses. However, nearly all of the secondary endpoints of response, such as various levels of response on the Assessment of SpondyloArthritis international Society criteria and the Ankylosing Spondylitis Disease Activity Score, were achieved significantly less often among patients who also had fibromyalgia.

Although BASDAI response was not different between the groups, the investigators said that fibromyalgia had a negative effect on TNF blocker response that “seems related to the instruments used in its evaluation rather than a different treatment effect of the molecule.”

Sensitivity analyses that used the 1990 American College of Rheumatology criteria to define the presence of fibromyalgia rather than the FiRST questionnaire result at baseline did not find any differences in TNF blocker responses between the groups on the main endpoint and most of the secondary endpoints. The ACR criteria classified fibromyalgia in 16.1% of the patients.

Another set of sensitivity analyses that used only the FiRST results at 12 weeks to diagnose fibromyalgia found that fibromyalgia patients had lower responses to treatment on nearly all endpoints. Only 18.7% of patients tested positive on the FiRST questionnaire at 12 weeks.

The change in C-reactive protein (CRP) levels at 12 weeks was not different between the groups of patients regardless of the definition used for fibromyalgia.

The researchers observed a decreased frequency of HLA-B27 positivity, radiographic sacroiliitis, and MRI sacroiliitis in people with both diseases. The authors called this finding “intriguing” and said it “might suggest that some patients participating in the trial might have been misdiagnosed and were in fact suffering from [fibromyalgia] only.”

But other clinical features suggestive of axSpA, such as uveitis, psoriasis, and inflammatory bowel disease, were equally present across the different groups.

Overall, “these results suggest that there is indeed an impact on the treatment response, but seems more related to the patient-reported outcomes used in the effectiveness endpoints, as suggested by the absence of difference across groups for the objective biological parameters (i.e., CRP).”

Dr. Moltó and her colleagues said their findings highlighted the importance not only of evaluating the presence of coexisting fibromyalgia in patients with axSpA when evaluating treatment response but also in determining treatment targets.

“This seems particularly important for decision of the treatment target in patients with axSpA when applying a treat-to-target strategy: For example, remission might not be a feasible target for these patients [with concomitant fibromyalgia] who will not likely reach this state, but should rather aim for a significant change or focus in only on objective parameters (i.e., CRP),” they concluded.

The study was funded by an unrestricted grant from Merck Sharp & Dohme. The authors declared having no competing interests.

SOURCE: Moltó A et al. Ann Rheum Dis. 2017 Nov 28. doi: 10.1136/annrheumdis-2017-212378 .


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