The prevalence and impact of comorbid fibromyalgia in inflammatory arthritis.

Fibromyalgia (FM) is one of the most common conditions that rheumatologists encounter. It is characterised by chronic widespread pain, fatigue, sleep disturbances and impaired cognition. The prevalence of comorbid FM among populations with rheumatoid arthritis (RA), axial spondyloarthritis (axSpA) and psoriatic arthritis (PsA) are considerably higher than among the general population, with pooled prevalence estimates of 18-24% in RA, 14-16% in axSpA and 18% in PsA. Prevalence estimates should be interpreted with care as the criteria for FM have not been validated for use in patients with inflammatory arthritis. Comorbid FM appears to affect assessment of disease severity in these conditions, particularly patient-reported outcome measures, and may influence response to treatment. There is a need for better identification, classification and management of FM in the context of inflammatory rheumatic diseases.