Background Fibromyalgia (FM) affects 12-17 percent of patients with Rheumatoid Arthritis (RA). It is previously shown that the DAS-28 score is significantly higher in RA patients with concomitant FM compared to RA patients without FM. This difference in the DAS-28 score is due to tender joint count and general VAS-score whereas objective parameters as swollen joint count and ESR seem equal in the two groups.
Objectives To investigate the prevalence of FM among RA patients in an outpatient rheumatology clinic, to compare the DAS-28 score in RA patients with and without FM, and to investigate if FM is associated with increased use of biological therapy against RA.
Methods Questionnaires1, which has been demonstrated to diagnose FM with a sensitivity of 93.1% and specificity of 91.7%, were handed out among RA patients during their planned visit to an outpatient rheumatology clinic. The DAS-28 score was noted from the DANBIO-registry and the patients' medical treatment, age, duration of disease, gender, serology-, smoking-, working- and marital status was noted from patients' files. The chi-square test was applied to investigate the difference in the use of biological therapy between the two groups. Unpaired T-tests were applied to compare the DAS-28, age, duration of disease, HAQ and VAS scores between the two groups.
Results 141 patients out of 199 filled out the questionnaire correctly, giving a response rate of 71%. Nineteen patients (13%) with concomitant FM were identified. No difference was found between the two groups regarding age, duration of disease, gender, serology, current smoking- and marital status. Sixty-eight percent of the FM patients were treated with biological therapy compared to 32% of patients without concomitant FM (p=0.002). The mean DAS 28-score among RA patients with concomitant FM was 4.51 compared to 3.02 (P<0.001). The elevated DAS-28 score in the FM group was due to tender joint count (p=0.011) and global VAS (p<0.001). Furthermore, HAQ-score and tired VAS were significantly higher in the FM group compared to the group without FM (p<0.001 for both comparisons). FM patients were more likely to have taken disability retirement than non-FM patients (p<0.001). Erosions were more pronounced in the non-FM group (p=0.03).
Conclusions Concomitant FM predicts higher DAS-28 scores in RA patients due to subjective parameters and is associated with a higher degree of biological treatment. These results suggest that FM could mislead the physician to overestimate the disease activity of RA patients and thereby to initiate therapy not indicated. More studies investigating this issue are warranted.
Ferrari R, Russell AS. A questionnaire using the Modified 2010 American College of Rheumatology criteria for fibromyalgia: Specificity and sensitivity in clinical practice. J Rheumatol 2013;40:1590-5.
Disclosure of Interest : None declared