Fibromyalgia, a missed comorbidity in spondyloarthritis: prevalence and impact on assessment and treatment

Purpose of review Fibromyalgia is a clinical representation of the neurobiological phenomenon of central sensitization, characterized by chronic widespread pain, fatigue, sleep disturbance, and other symptoms. Fibromyalgia may occur in conjunction with chronic rheumatic diseases, driven by the effects of chronic pain and inflammation and likely influenced by the patient's genetic and psychoemotional background. This article reviews the data on prevalence of concomitant fibromyalgia and its impact on disease assessment in patients with spondyloarthritis (SpA) and psoriatic arthritis (PsA). Recent findings Fibromyalgia occurs in 2-8% of the general population. In AxSpA cohorts the prevalence has been reported in 4-25%, and in PsA, 16-22%, the majority being female. Measures of disease activity which are comprised partly or wholly of patient-reported outcomes such as pain and patient global are significantly higher in patients with concomitant fibromyalgia and do not improve as much with treatment as more objective measures, a finding which has been observed in other diseases such as rheumatoid arthritis and lupus. Summary Fibromyalgia occurs in a significant proportion of patients with SpA and PsA. Disease activity measures with subjective elements are conflated in patients with fibromyalgia and do not reliably assess true inflammatory disease. This needs to be taken into account when evaluating the impact of immunomodulatory therapy.