Fibromyalgia with concomitant immune-mediated rheumatic diseases: an evaluation of clinical characteristics,...

Fibromyalgia (FM) is a relevant comorbidity in immune-mediated rheumatic diseases (IMRD). Immune mechanisms have been postulated to trigger FM, potentially leading to distinct clinical features compared to FM occurring without IMRDs. This study aims to provide a comprehensive comparison of FM characteristics in patients with and without concomitant IMRD and to evaluate the differences in diagnostic FM criteria between the two groups.

A comprehensive dataset of clinical, psychosocial, and sleep variables, along with validated questionnaires, was prospectively collected from 341 patients with chronic musculoskeletal pain syndromes who participated in a rheumatology-led, two-week multimodal inpatient program at the University Hospital of Lausanne between 2018 and 2024. Participants were included if they met either the Fibromyalgia Rapid Screening Tool (FiRST) or the American College of Rheumatology (ACR) 2010 criteria for FM. The disease activity of the underlying IMRD was assessed by two rheumatologists. Data were separately analyzed in two cohorts: one fulfilling the FiRST criteria and the other fulfilling the ACR 2010 criteria.

Among the participants, 153 patients met the FiRST criteria, of whom 34 also had a history of clinically diagnosed IMRD. Similarly, 149 patients fulfilled the ACR 2010 criteria, with 32 of them also having IMRD. The most common IMRDs were HLA-B27-negative spondyloarthritis (53%), Sjögren's syndrome (16%), HLA-B27-positive spondyloarthritis (9%), psoriatic arthritis (9%), seronegative rheumatoid arthritis (9%), and seropositive rheumatoid arthritis (3%). In 88% of patients with IMRD, the disease was considered inactive. No significant clinical or epidemiological differences were found between FM patients with or without IMRD in either the FiRST or ACR 2010 cohorts, except for a higher prevalence of enthesopathies and childhood pain in patients with concomitant IMRD. FM patients with IMRD had slightly lower FiRST scores, and FiRST-positive IMRD patients showed a better short-term response to the multimodal program, particularly in FABQ-work, BPI-interference, and Pain Catastrophizing Scale scores. However, no significant difference was observed in the Pain Disability Index (PDI) three months post-program.

HLA-B27-negative spondyloarthritis and Sjögren's syndrome were the most common concomitant IMRDs in this FM cohort. FM patients with and without IMRD exhibited similar clinical and epidemiological features, suggesting a common pathophysiological background. The FiRST criteria, which emphasize central hypersensitization rather than diffuse pain, appear to be a suitable tool for detecting FM in IMRD patients. This may be particularly useful in cases where enthesial pain might interfere with FM diagnosis, and vice versa.