E2 ModerateModerate confidencePEM not requiredLongitudinalPeer-reviewedReviewed
Natural course of symptoms in Cambodia veterans: a follow-up study.
De Vries, M, Soetekouw, P M, Van Der Meer, J W et al. · Psychological medicine · 2001 · DOI
Quick Summary
Researchers followed Dutch military veterans who served in Cambodia in 1992-1993 and reported fatigue and memory problems after returning home. At 18 months later, about 39% of veterans reported feeling much better or completely recovered, while 57% still had the same symptoms and 4% felt worse. The study found that veterans who started with less severe fatigue and felt they had more control over their symptoms were more likely to improve.
Why It Matters
This study provides prognostic data on the natural course of post-deployment fatigue syndromes, identifying factors associated with recovery versus chronic symptom persistence. The finding that perceived control and initial symptom severity predict outcomes has direct relevance to understanding ME/CFS trajectories and informs potential psychological intervention targets for chronically fatigued patients.
Observed Findings
- At 18-month follow-up, 19% of veterans reported complete recovery and 20% reported much improvement, while 57% had unchanged complaints and 4% worsened.
- Lower initial fatigue severity was a significant predictor of self-reported improvement and lower fatigue levels at follow-up.
- Greater perceived control over symptoms at baseline predicted better outcomes at follow-up.
- A substantial portion of Cambodia veterans (61%) continued to experience severe fatigue and related symptoms despite the passage of 18 months.
Inferred Conclusions
- Self-reported improvement occurs in a clinically significant minority of post-deployment fatigue cases, but symptom persistence is common, suggesting heterogeneous prognosis.
- Perceived control and initial symptom severity are modifiable and measurable factors that predict differential recovery in chronic fatigue syndromes.
- Prognostic patterns in Cambodia veterans may parallel those in Gulf War illness and ME/CFS, suggesting common underlying prognostic mechanisms across post-exposure fatigue syndromes.
Remaining Questions
- What mechanisms explain why perceived control predicts better outcomes—is this protective psychologically, or does it reflect actual biological differences in disease severity?
- Why do 57% of veterans maintain stable symptoms over 18 months—are these truly persistent cases or do longer follow-up periods show delayed recovery?
What This Study Does Not Prove
This study does not establish causation or mechanism—it describes associations between baseline factors and later outcomes in a specific military population. The findings cannot be directly generalized to ME/CFS patients without validation in that cohort, and the study does not prove that fatigue severity or perceived control *cause* improvement, only that these factors are correlated with it.
Tags
Symptom:Cognitive DysfunctionFatigue
Method Flag:PEM Not DefinedWeak Case DefinitionNo ControlsExploratory Only
Metadata
- DOI
- 10.1017/s0033291701003075
- PMID
- 11232919
- Review status
- Editor reviewed
- Evidence level
- Single-study or moderate support from human research
- Last updated
- 12 April 2026
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 →
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