First-night effect in the chronic fatigue syndrome.
Le Bon, Olivier, Minner, Pierre, Van Moorsel, Cédric et al. · Psychiatry research · 2003 · DOI
Quick Summary
When people with ME/CFS spend a night in a sleep lab, their sleep patterns often change between the first and second night—a phenomenon called the 'first-night effect.' This study found that ME/CFS patients do experience this adaptation effect, where sleep measurements like total sleep time and sleep quality improve on the second night. Understanding this pattern helps doctors interpret sleep test results more accurately.
Why It Matters
Sleep disturbance is a cardinal feature of ME/CFS, yet clinical sleep assessments rely on polysomnography data that may be confounded by laboratory adaptation. This study demonstrates that ME/CFS belongs to a class of medical conditions where first-night effects are clinically meaningful, informing best practices for sleep study interpretation and highlighting the need for standardized recording protocols in ME/CFS research.
Observed Findings
Multiple polysomnographic parameters differed significantly between night 1 and night 2, including total sleep time, sleep efficiency, sleep onset latency, slow-wave sleep, REM sleep, and REM latency.
Bland-Altman analysis revealed systematic bias linked to recording order (first-night effect).
Three distinct factors emerged from factorial analysis of night-to-night difference scores.
Psychiatric comorbidity (generalized anxiety or other disorders) did not significantly influence the magnitude of first-night effect.
ME/CFS patients exhibited habituation patterns comparable to other medical conditions, not exclusive to sleep disorders.
Inferred Conclusions
ME/CFS must be added to the list of medical conditions where a clinically significant habituation effect occurs during laboratory polysomnography.
The first-night effect in ME/CFS is independent of psychiatric comorbidity status.
Standardized two-night recording methodology may be optimal for accurate sleep assessment in ME/CFS.
Recording methodology substantially influences the interpretation of sleep parameters in this population.
Remaining Questions
Why does the first-night effect occur in some ME/CFS patients but not others?
What This Study Does Not Prove
This study does not establish the cause of sleep dysfunction in ME/CFS, nor does it prove that first-night effects are universal across all ME/CFS patients—the authors explicitly noted the effect was present in some cases but not others. The cross-sectional observational design cannot determine whether the habituation effect reflects true physiology or is purely a laboratory artifact, and the small sample size limits generalizability.
Tags
Symptom:Unrefreshing SleepFatigue
Method Flag:Weak Case DefinitionNo ControlsExploratory Only
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 →