Why Fibromyalgia Criteria Keep Changing: A Systematic Review of Misclassification, Measurement, and Diagnostic Spillover

Background/Aims: Fibromyalgia is diagnosed without a definitive biomarker, so classification and diagnostic criteria carry unusual clinical and epidemiologic weight. This Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020–guided systematic review examined why fibromyalgia criteria keep changing and how those changes influence overdiagnosis, misdiagnosis, missed diagnosis, chronic widespread pain boundaries, comorbid rheumatic disease, sex ratios, vitamin D deficiency, and prevalence estimates.

Materials and Methods: MEDLINE/PubMed, Scopus, and Web of Science Core Collection were searched from January 1, 1990 to March 4, 2026. Backward and forward citation tracking was added. Eligible records included criteria papers, validation and concordance studies, prevalence studies, health-system analyses, comorbidity studies, and digital or bodymap measurement studies. Fifty-eight records were included in the qualitative synthesis. Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) and Risk of Bias In Non-Randomized Studies of Interventions (ROBINS-I)-informed domains guided appraisal where appropriate.

Results: Across criteria eras, revisions redistributed rather than eliminated diagnostic error. The 1990 criteria standardized research cohorts but depended on tender-point examination. The 2010/2011 criteria improved feasibility and symptom capture, yet increased vulnerability to regionalpain and high-distress misclassification. The 2016 revision introduced a generalized pain requirement and clarified that fibromyalgia can coexist with other disorders, improving boundary control but not resolving clinician- criteria discordance, sex-sensitive under-recognition, or comorbidityrelated diagnostic delay. Prevalence estimates vary partly because criteria architecture, sampling frame, pain-map methods, and case-finding purpose differ across studies.

Conclusion: The 2016 criteria remain useful, but they are not a complete clinical diagnostic system. Future work should not merely add another threshold; it should combine generalized pain verification, dimensional severity reporting, comorbidity-aware interpretation, sex-sensitive screening, and explicit separation of chronic widespread pain from fibromyalgia.

Cite this article as: Gür A. Why fibromyalgia criteria keep changing: A systematic review of misclassification, measurement, and diagnostic spillover. Arch Rheumatol. 2026;41(3):155-167.