Heyll, U, Wachauf, P, Senger, V et al. · Medizinische Klinik (Munich, Germany : 1983) · 1997 · DOI
In 1988, doctors created an official definition for chronic fatigue syndrome (CFS) to help researchers study it consistently. However, this study found that the original definition didn't work as well as hoped—it didn't capture the condition accurately, and patients with CFS turned out to be quite different from each other. The authors suggest that CFS should be understood as a descriptive condition rather than a single disease with one cause.
This work highlights a fundamental challenge in ME/CFS research: heterogeneity among patients makes it difficult to establish consistent diagnostic criteria and understand disease mechanisms. Recognizing that CFS patients are not a uniform group is crucial for developing better diagnostic approaches and tailored treatments that account for individual differences.
This review does not identify specific biomarkers, genetic factors, or infections causing ME/CFS. It does not demonstrate what the underlying mechanisms are—only that the 1988 definition was inadequate for capturing them. It also does not establish which modified definitions or diagnostic approaches should replace the original criteria.
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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