Frequency of concomitant fibromyalgia in rheumatic diseases: Monocentric study of 691 patients

Fibromyalgia (FM) is a confounding factor for diagnosing and assessing rheumatic disease activity. This study sought to assess the extent of this syndrome in rheumatism patients at a French rheumatology department.

This monocentric epidemiological study enrolled all patients consulting due to rheumatoid arthritis (RA), spondyloarthritis (SpA), or connective tissue disease (CTD). FM diagnosis was confirmed or excluded according to the rheumatologist opinion and the 1990 American College of Rheumatology (ACR) criteria.

We enrolled 691 patients, including 451 women (65.3%), with a mean age of 55.8 years (18-93). Of the enrolled patients, 325 presented with RA, 298 SpA [59 psoriatic arthritis (PsA), 137 ankylosing spondylitis (AS), 64 non-radiographic SpA (nr-SpA), and 38 peripheral SpA], and 71 CTD. The rheumatologist established FM diagnosis in 97 patients (14%), while 55 (8%) fulfilled the 1990 ACR criteria. The frequency of FM was lower in RA patients (4.9% by 1990 ACR criteria; 7.7% by expert opinion) compared to SpA (11.1% by 1990 ACR, p < 0.05; 17.5% by expert opinion, p < 0.003) and CTD (11.3% by 1990 ACR, non-significant; 28.2% by expert opinion, p < 0.001). In the SpA subgroups, FM was more common in the nr-SpA than in PsA or AS (23.9%, 9.6%, and 6.4%, by 1990 ACR, p = 0.001; 37.3%, 13.5%, and 7.2%, by expert opinion, p < 0.001).

FM-like symptoms are commonly associated with rheumatic diseases. The frequency of FM is particularly high in non-radiographic axial SpA, thus raising questions about the specificity of the Assessment of SpondyloArthritis International Society (ASAS) classification criteria.