Clinical, immunological and metabolomic risk factors associated with fibromyalgia in a cohort of patients with idiopathic inflammatory myopathies

Objective To investigate the clinical, immunological, and metabolomic factors associated with fibromyalgia (FM) in patients with idiopathic inflammatory myopathies (IIM) who are in clinical remission or complete response. Methods In this cross-sectional, 49 patients with IIM meeting remission and/or complete clinical response criteria were evaluated with the PROMIS Pain Interference Short Form 8a as an initial screening tool and patients with clinically significant pain interference subsequently underwent assessment with the 2016 ACR criteria. Clinical data, flow cytometry of peripheral blood mononuclear cells, multiplex cytokine assays, and untargeted metabolomic profiling by GC-MS were performed. Multivariate logistic regression was used to identify variables associated with FM. Results The prevalence of FM in this IIM cohort was 40.8%. FM was associated with higher patient global assessment scores, increased muscle damage, current prednisone use, and elevated serum levels of IL-6 and MCP-1. Immunophenotyping revealed reduced numbers of non-classical monocytes, CD8 + T cells, and B lymphocytes in FM patients. Metabolomic analysis identified lower concentrations of tryptophan and nonanoic acid in the FM group, suggesting altered pathways of immune regulation and nociplastic pain. Conclusion Patients with IIM in remission and/or complete clinical response can present with clinical significant FM, which is associated with immune dysregulation and metabolic alterations. These findings highlight the need for routine FM screening in IIM and support the use of patient-reported outcomes to distinguish between inflammatory and nociplastic symptoms in clinical practice.