Concomitant fibromyalgia in rheumatoid arthritis is associated with the more frequent use of biological therapy: a cross-sectional study.

Objectives: To compare the 28-joint Disease Activity Score (DAS28) and its components in patients with rheumatoid arthritis (RA) with and without concomitant fibromyalgia (FM), and to investigate the use of biological treatment in the two groups.
Method: Questionnaires developed to diagnose FM were handed out among RA patients during their planned visits. Values for DAS28 were obtained from the DANBIO registry. Demographic data and data on patients' medical treatment, disease duration, serological and radiological status were retrieved from patients' files. The χ ² test and an unpaired t-test were applied to investigate group differences in the use of biological therapy, baseline characteristics, patient-reported outcomes, and DAS28 between groups when appropriate.
Results: Questionnaires were completed by 162 out of 264 (61%) patients. Twenty-five patients (15.4%) with concomitant FM were identified. No group differences were found regarding disease duration, age, gender, and serological status. Of the RA patients with concomitant FM, 64% were treated with biological therapy vs. 32% of RA patients without concomitant FM (p = 0.002). The mean DAS28 in the FM group was 4.4 compared to 2.9 in the non-FM group (p < 0.001). Elevated DAS28 in the FM group resulted from a high tender joint count (p = 0.003) and a high visual analogue scale (VAS)-global score (p < 0.001). Erosions were more frequent in the non-FM group (p = 0.04).
Conclusions: Concomitant FM in patients with RA is associated with a higher DAS28 due to subjective parameters and with the more frequent use of biological treatments. This raises the question of whether the more frequent use of biologics in these patients is justified by inflammation, or is instead due to persistent pain and other centrally mediated symptoms.