Nisenbaum, Rosane, Reyes, Michele, Unger, Elizabeth R et al. · Journal of psychosomatic research · 2004 · DOI
This study looked at 1,391 people with unexplained chronic fatigue to understand which symptoms tend to occur together. Researchers found that ME/CFS symptoms cluster into three main groups: muscle and joint pain, infection-like symptoms, and problems with thinking, mood, and sleep. Interestingly, people with and without an ME/CFS diagnosis had significant overlap in these symptoms, suggesting that ME/CFS exists on a spectrum rather than as a completely distinct condition.
This study is important because it challenges the idea that ME/CFS is a completely separate condition from other unexplained fatigue disorders, suggesting instead that it exists on a continuum. Understanding that ME/CFS symptoms overlap significantly with other conditions can help improve research design and may eventually lead to better identification of meaningful biological subtypes rather than relying solely on symptom-based definitions.
This study does not identify the causes of ME/CFS or prove that ME/CFS and other unexplained fatigue syndromes are the same condition—it only shows symptom overlap. It also does not establish biological or genetic markers that distinguish between groups, nor does it prove that symptom overlap means these conditions should be grouped together for treatment purposes.
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
Nisenbaum, Rosane, Reyes, Michele, Unger, Elizabeth R, & Reeves, William C (2004). Factor analysis of symptoms among subjects with unexplained chronic fatigue: what can we learn about chronic fatigue syndrome?. Journal of psychosomatic research. https://doi.org/10.1016/S0022-3999(03)00039-4
BibTeX
@article{mecfsatlas-nisenbaum-2004-factor-analysis,
author = {Nisenbaum, Rosane and Reyes, Michele and Unger, Elizabeth R and Reeves, William C},
title = {Factor analysis of symptoms among subjects with unexplained chronic fatigue: what can we learn about chronic fatigue syndrome?},
journal = {Journal of psychosomatic research},
year = {2004},
doi = {10.1016/S0022-3999(03)00039-4},
note = {PubMed: 15016574},
url = {https://www.mecfsatlas.com/evidence/nisenbaum-2004-factor-analysis},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-28. https://www.mecfsatlas.com/evidence/nisenbaum-2004-factor-analysis
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