van der Werf, S P, Prins, J B, Jongen, P J et al. · Neuropsychiatry, neuropsychology, and behavioral neurology · 2000
This study compared how people with ME/CFS and people with multiple sclerosis (MS) performed on memory and thinking tests. The researchers found that people with ME/CFS were more likely to show signs of reduced effort on memory tests, but both groups had similar rates of poor performance on standard cognitive tests. This suggests that poor test results in ME/CFS patients might sometimes reflect how hard they're trying during the test, rather than actual brain damage.
This study highlights a critical methodological issue: cognitive complaints in ME/CFS may not always reflect brain damage, and testing methods must distinguish between true neurologic impairment and reduced test-taking effort. This has important implications for how clinicians and researchers interpret cognitive deficits in ME/CFS and for designing fair diagnostic criteria.
This study does not prove that ME/CFS patients are malingering or that their cognitive symptoms are not real. It also does not establish whether reduced effort reflects motivational factors, disease-related fatigue, or other biological mechanisms. The cross-sectional design cannot determine causation or whether effort patterns change over time.
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
van der Werf, S P, Prins, J B, Jongen, P J, van der Meer, J W, & Bleijenberg, G (2000). Abnormal neuropsychological findings are not necessarily a sign of cerebral impairment: a matched comparison between chronic fatigue syndrome and multiple sclerosis.. Neuropsychiatry, neuropsychology, and behavioral neurology. https://pubmed.ncbi.nlm.nih.gov/10910092/
BibTeX
@article{mecfsatlas-van-der-werf-2000-abnormal-neuropsychological,
author = {van der Werf, S P and Prins, J B and Jongen, P J and van der Meer, J W and Bleijenberg, G},
title = {Abnormal neuropsychological findings are not necessarily a sign of cerebral impairment: a matched comparison between chronic fatigue syndrome and multiple sclerosis.},
journal = {Neuropsychiatry, neuropsychology, and behavioral neurology},
year = {2000},
note = {PubMed: 10910092},
url = {https://www.mecfsatlas.com/evidence/van-der-werf-2000-abnormal-neuropsychological},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-28. https://www.mecfsatlas.com/evidence/van-der-werf-2000-abnormal-neuropsychological
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