Fibromyalgic rheumatoid arthritis and disease assessment

Objective. We evaluated fibromyalgic RA to determine its clinical impact, identification using core clinical assessments and influence identifying active disease using disease activity scores (DAS-28). Methods. We examined the impact and identification using core clinical assessments (tender minus swollen joint counts) of fibromyalgic RA (≥11 tender points) in initial (105 patients) and replicate (100 patients) cohorts. Receiver operator characteristic (ROC) curves optimized the cut-off points using tender minus swollen joint counts; their validity was confirmed in a routine practice cohort (321 patients). We evaluated whether fibromyalgic RA affected the identification of active disease using DAS-28 (≥5.1) and the clinical disease activity index (CDAI). Results. A total of 18/105 and 12/100 patients in initial and replicate cohorts, respectively, had fibromyalgic RA. This was identified by ≥7 tender minus swollen joint counts with 83% sensitivity and 80% specificity in the initial cohort (72 and 98% in replicate, respectively) and ROC area under the curve 0.80 (0.94 in replicate). 'Fibromyalgic' RA (tender point scores in initial and tender minus swollen joints in clinical practice cohorts) had higher DAS-28, pain, fatigue and HAQ scores. More fibromyalgic RA patients had active disease by DAS-28 (odds ratio 14.3; 95% CI 5.5, 37.1; and CDAI 17.2; 95% CI 6.1, 48.5); conventional assessments (three or more tender joints; three or more swollen joints; ESR ≥ 28 mm/h) showed no difference (1.75; 95% CI 0.72, 4.3). Conclusion. Fibromyalgic RA affects 12-17% of RA outpatients and results in worse functional outcomes. DAS-28 scores over-interpret active disease in fibromyalgic RA.