Associations between Microbiome Diversity and Fibromyalgia or Myalgia: A Systematic Review and Meta-Analysis

INTRODUCTION: Recent evidence points out that alterations in gut microbiome may be associated with pain modulation in fibromyalgia (FM). The objective was to review the associations between microbiome diversity and FM or chronic widespread pain (CWP), to identify microbial taxa consistently altered in affected individuals and to quantify the alpha diversity change in fibromyalgia.
METHODS: In systematic search conducted through PubMed, Scopus and Google Scholar for studies published between 2010 and September 2025 using synonyms of “fibromyalgia”, “chronic pain syndrome” and “microbiome” was undertaken. Eligible studies reporting microbiome diversity metrics with Shannon index or alpha diversity in adult FM/CWP patients compared with healthy controls were selected. Random-effects meta-analysis was performed for alpha diversity outcomes using standardized mean differences (SMD). Heterogeneity and risk of bias were assessed using established methods.
RESULTS: Overall, nine studies met inclusion criteria and Shannon-diversity index was extracted from seven studies (2233 participants). FM patients exhibited significant reduction in gut microbiota diversity with compared with controls (SMD -0.40, 95% CI -0.55 to -0.25; p < 0.001), with between the study heterogeneity was low (I² = 13.8%). Qualitative synthesis revealed consistent depletion of butyrate-producing taxa, including Faecalibacterium and Coprococcus, and enrichment of taxa linked to pro-inflammatory and neuroactive pathways, such as Parabacteroides merdae and Clostridium scindens.
DISCUSSION AND CONCLUSION: FM is associated with consistent reduction in gut microbiome alpha diversity. There are consistent shifts in important microbial taxa. Findings from this review support the potential role of microbiome dysbiosis in FM pathophysiology and highlight the potential role of microbiome based biomarkers and therapeutic strategies.

Keywords: myalgia, meta-analysis, chronic pain, fibromyalgia, microbiota, butyrates