Wilson, A, Hickie, I, Hadzi-Pavlovic, D et al. · The Australian and New Zealand journal of psychiatry · 2001 · DOI
This study looked at 744 people with chronic fatigue across eight countries to see if they formed different groups based on their symptoms. Researchers found two distinct subgroups: a larger group (68%) with less severe illness and fewer psychiatric issues, and a smaller group (32%) whose symptoms looked more like somatoform illness (where psychological factors strongly influence physical symptoms). Importantly, the proportion of people in each group varied dramatically between countries (6-48%), suggesting that how doctors diagnose and classify ME/CFS is not standardized worldwide.
This study is crucial because it demonstrates that ME/CFS is not a single disease entity but a heterogeneous condition encompassing at least two clinically distinct subgroups. Understanding this variability is essential for designing better clinical trials, identifying which patients might benefit from different treatments, and explaining why international diagnostic criteria produce inconsistent patient populations.
This study does not prove that the two identified subgroups have different biological causes or will respond differently to specific treatments. The cross-sectional design cannot establish whether subclass membership predicts prognosis or treatment outcomes, nor does it clarify whether the variation between centres reflects true epidemiological differences or differences in how doctors apply diagnostic 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 →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Wilson, A, Hickie, I, Hadzi-Pavlovic, D, Wakefield, D, Parker, G, Straus, S E, et al. (2001). What is chronic fatigue syndrome? Heterogeneity within an international multicentre study.. The Australian and New Zealand journal of psychiatry. https://doi.org/10.1046/j.1440-1614.2001.00888.x
BibTeX
@article{mecfsatlas-wilson-2001-what-chronic,
author = {Wilson, A and Hickie, I and Hadzi-Pavlovic, D and Wakefield, D and Parker, G and Straus, S E and Dale, J and McCluskey, D and Hinds, G and Brickman, A and Goldenberg, D and Demitrack, M and Blakely, T and Wessely, S and Sharpe, M and Lloyd, A},
title = {What is chronic fatigue syndrome? Heterogeneity within an international multicentre study.},
journal = {The Australian and New Zealand journal of psychiatry},
year = {2001},
doi = {10.1046/j.1440-1614.2001.00888.x},
note = {PubMed: 11531735},
url = {https://www.mecfsatlas.com/evidence/wilson-2001-what-chronic},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-25. https://www.mecfsatlas.com/evidence/wilson-2001-what-chronic
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