The incidence of fibromyalgia and its associated comorbidities: a population-based retrospective cohort study based on International Classification of Diseases, 9th Revision codes. — ME/CFS Atlas
E2 ModerateModerate confidencePEM not requiredObservationalPeer-reviewedReviewed
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The incidence of fibromyalgia and its associated comorbidities: a population-based retrospective cohort study based on International Classification of Diseases, 9th Revision codes.
Weir, Peter T, Harlan, Gregory A, Nkoy, Flo L et al. · Journal of clinical rheumatology : practical reports on rheumatic & musculoskeletal diseases · 2006 · DOI
Quick Summary
This study looked at how often fibromyalgia is diagnosed in a large group of insured people over a 6-year period. The researchers found that fibromyalgia is diagnosed more often in women than men, though not as dramatically as previous studies suggested. People with fibromyalgia were much more likely to also have other conditions like depression, anxiety, headaches, irritable bowel syndrome, chronic fatigue syndrome, lupus, and rheumatoid arthritis.
Why It Matters
This study is significant for ME/CFS patients because it establishes strong epidemiological associations between fibromyalgia and chronic fatigue syndrome as comorbid conditions, suggesting shared pathophysiological mechanisms or overlapping disease processes. Understanding the incidence and comorbidity patterns of fibromyalgia helps clarify the broader landscape of chronic conditions that frequently co-occur with ME/CFS, which may inform diagnostic and treatment approaches.
Observed Findings
2,595 incident fibromyalgia cases were identified over the 6-year study period in a large insurance claims database.
Age-adjusted incidence was 6.88 cases per 1,000 person-years in males and 11.28 cases per 1,000 person-years in females.
Females were 1.64 times more likely than males to receive a fibromyalgia diagnosis.
Patients with fibromyalgia were 2.14–7.05 times more likely to have at least one of seven comorbid conditions (depression showing strongest association, SLE weakest).
Chronic fatigue syndrome was among the seven comorbid conditions most strongly associated with fibromyalgia.
Inferred Conclusions
Fibromyalgia shows a female predominance, although substantially less pronounced than previously reported in prevalence studies.
Strong bidirectional associations exist between fibromyalgia and multiple chronic conditions, suggesting shared underlying pathways or diagnostic overlap.
The consistent comorbidity patterns suggest that fibromyalgia may be part of a broader syndrome rather than an isolated disorder.
Remaining Questions
Does the female-to-male ratio of 1.64 reflect true biological sex differences or diagnostic bias (women more likely to seek care or receive diagnosis)?
What This Study Does Not Prove
This study does not establish causality between fibromyalgia and its associated comorbidities—it only documents that they occur together more frequently than by chance. It cannot explain whether fibromyalgia causes these conditions, these conditions cause fibromyalgia, or whether shared underlying biological mechanisms link them. The study also does not validate diagnostic accuracy or assess whether coding errors affected the incidence estimates.
Tags
Symptom:PainFatigue
Method Flag:PEM Not DefinedWeak Case DefinitionMixed CohortNo Controls
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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