Lloyd, A R · The American journal of medicine · 1998 · DOI
This review examines how fatigue is defined and diagnosed, and how different definitions lead to very different estimates of how many people have chronic fatigue syndrome. The authors look at how doctors and researchers measure fatigue using patient reports, and explore whether fatigue that follows infections is a real medical condition. The study highlights that without clear, consistent definitions, it's difficult to understand the true scope of the problem.
This study is important because it reveals a fundamental challenge in ME/CFS research: inconsistent definitions lead to conflicting findings about prevalence, causes, and outcomes. Understanding how diagnostic boundaries affect research results helps patients and clinicians recognize why there's sometimes disagreement in the medical literature. This work laid groundwork for later efforts to standardize CFS diagnostic criteria.
This review does not establish the biological mechanisms underlying ME/CFS, nor does it prove whether postinfective fatigue is a distinct disease entity. It documents the problem of variable definitions but does not propose a definitive solution or validate any single diagnostic approach. The reliance on self-reported data means it does not establish objective biomarkers for the condition.
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
Lloyd, A R (1998). Chronic fatigue and chronic fatigue syndrome: shifting boundaries and attributions.. The American journal of medicine. https://doi.org/10.1016/s0002-9343(98)00157-0
BibTeX
@article{mecfsatlas-lloyd-1998-chronic-fatigue,
author = {Lloyd, A R},
title = {Chronic fatigue and chronic fatigue syndrome: shifting boundaries and attributions.},
journal = {The American journal of medicine},
year = {1998},
doi = {10.1016/s0002-9343(98)00157-0},
note = {PubMed: 9790475},
url = {https://www.mecfsatlas.com/evidence/lloyd-1998-chronic-fatigue},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/lloyd-1998-chronic-fatigue
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