Thomas, Marie, Smith, Andrew · The open neurology journal · 2009 · DOI
This study tested whether people with ME/CFS have real problems with thinking and memory, not just imagine they do. The researchers gave a large group of properly diagnosed ME/CFS patients a thorough set of cognitive tests and found clear evidence of cognitive difficulties. Importantly, these problems were not caused by depression or anxiety, suggesting they are a direct part of the illness.
This research validates a core complaint of ME/CFS patients—that cognitive difficulties are real and measurable, not psychological in origin. By demonstrating that proper testing reveals objective deficits independent of mood disorders, the study strengthens the case for cognitive impairment as a biological feature of ME/CFS rather than a psychiatric symptom, potentially improving recognition and clinical evaluation of this symptom.
This study does not identify the biological mechanisms causing cognitive impairment in ME/CFS, nor does it establish whether cognitive deficits are present from disease onset or develop over time. The cross-sectional design means the study cannot determine causation or establish whether treatment actually causes improvement versus natural recovery.
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
Thomas, Marie & Smith, Andrew (2009). An investigation into the cognitive deficits associated with chronic fatigue syndrome.. The open neurology journal. https://doi.org/10.2174/1874205X00903010013
BibTeX
@article{mecfsatlas-thomas-2009-investigation-into,
author = {Thomas, Marie and Smith, Andrew},
title = {An investigation into the cognitive deficits associated with chronic fatigue syndrome.},
journal = {The open neurology journal},
year = {2009},
doi = {10.2174/1874205X00903010013},
note = {PubMed: 19452031},
url = {https://www.mecfsatlas.com/evidence/thomas-2009-investigation-into},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/thomas-2009-investigation-into
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