E0 ConsensusModerate confidencePEM not requiredReview-NarrativePeer-reviewedMachine draft
A review of the evidence for overlap among unexplained clinical conditions.
Aaron, L A, Buchwald, D · Annals of internal medicine · 2001 · DOI
Quick Summary
This review examined eight unexplained illnesses—including ME/CFS, fibromyalgia, and irritable bowel syndrome—and found they share many similarities in symptoms (like fatigue and pain), how they affect daily life, and how they respond to laboratory tests. The researchers discovered that many patients have more than one of these conditions at the same time, suggesting they may be related or overlap in important ways.
Why It Matters
This review provides evidence that ME/CFS does not exist in isolation but shares significant features with other poorly understood illnesses, suggesting a common underlying mechanism may link these conditions. Understanding these overlaps helps clinicians recognize that patients with one condition should be screened for others, and supports the need for research focused on shared pathophysiology rather than isolated syndromes.
Observed Findings
- Many patients diagnosed with one unexplained clinical condition met diagnostic criteria for a second unexplained condition.
- Tender points on physical examination and decreased pain threshold/tolerance were the most frequent and consistent objective findings across conditions.
- Case definitions and symptom presentations showed substantial similarities across the eight examined conditions.
- Laboratory abnormalities were inconsistently demonstrated across studies.
- All eight conditions shared features of disability disproportionate to physical examination findings.
Inferred Conclusions
- Unexplained clinical conditions show substantial overlap in symptoms, disability patterns, and objective findings, suggesting possible shared mechanisms.
- Existing explanatory models are inadequate because they cannot account for the high prevalence of multiple unexplained conditions occurring simultaneously in individual patients.
- Methodologic standardization in case definition and study design is essential for future research to clarify relationships among these conditions.
Remaining Questions
- What is the biological mechanism underlying the overlap among these unexplained clinical conditions?
- Does the overlap reflect one underlying disease with variable presentations, or multiple distinct diseases sharing common features?
What This Study Does Not Prove
This review does not establish causation or a single unifying biological cause for these overlapping conditions. It also does not prove that psychosocial factors cause these illnesses—only that they are statistically associated with them—and does not resolve whether these are distinct diseases or variations of one underlying condition.
Tags
Symptom:PainFatigue
Biomarker:Blood Biomarker
Method Flag:PEM Not DefinedWeak Case DefinitionMixed Cohort
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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