Fibromyalgia in patients with rheumatoid arthritis: driven by depression or joint damage?

Objectives. Studies have shown an increased incidence of fibromyalgia (FMS) in RA patients'. The aims of this study were to explore the effect of mood and disease damage on the prevalence of FMS. Methods. RA patients underwent a standardised clinical assessment, including disease activity (DAS-28), disease damage (mechanical joint score, MJS), fibromyalgia tender point assessment and the Hospital Anxiety and Depression Scale (HADS) and Health Assessment Questionnaire (HAQ). Patients were classified with FMS using two criteria a) tender-swollen joint count was >= 7 or b) tender point score of >= 11/18. Results. 44/285 (15%) patients were classified as having EMS using the joint count difference of >= 7, compared to 18/285 (6%) using the tender point score of >11. Using the joint count difference to classify patients as having FMS, those with FMS had higher HAQ scores than those without FMS (2.12 vs. 1.5, p<0.0001). Although the DAS-28 was higher in this group (5.4 vs. 3.82, p<0.0001), the MJS was similar (8 vs. 7, p=0.19), suggesting similar levels of joint damage. Those classified as having EMS were more likely to have HAD-D scores of >11 (25% vs. 6%, p=0.0001). Conclusions. Coexistent FMS was common in our cohort, although using the tender point count to define FMS classified fewer patients with FMS. Within this group those with FMS had higher levels of depression but similar scores for joint damage indicating that in this cohort FMS and poorer physical functioning is mediated by low mood rather than joint damage.