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Measurement of excessive daytime sleepiness

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Measurement of excessive daytime sleepiness

  • important to distinguish excessive daytime sleepiness (EDS) from fatigue
    • EDS is defined as the inability to maintain wakefulness and alertness during the major waking episodes of the day, with sleep occurring unintentionally or at inappropriate times almost daily for at least three months (2)
      • is used interchangeably with hypersomnia and hypersomnolence
      • according to ICD-4
        • hypersomnolence is excessive sleepiness when wakefulness is expected, and hypersomnia is a disorder characterised by hypersomnolence

  • Epworth sleepiness scale (ESS) is a measure of daytime sleepiness that is developed for and used in a range of sleep disorders
    • for the ESS assessment
      • the patient is asked to rate their likelihood of dozing or falling asleep in response to eight common situations on a scale of 0 to 3:
      • 0 being no chance of dozing off and 3 high chance
      • overall scores above 10 are generally accepted to represent excessive daytime sleepiness (EDS)
      • ESS >10 indicates EDS and >17 indicates severe EDS

  • the gold standard physiological evaluation is the multiple sleep latency test (MSLT) (used in a specialist sleep setting)
    • provides objective measurement of rapidity of sleep onset
    • MSLT measures an individual’s physiologic sleep tendency when potential alerting environmental or circadian cues are controlled. One of the main advantages of this test is that the degree of sleepiness cannot be exaggerated by the patient. Sleep latency is assessed over five daytime nap trials of 20 minutes each, at two hour intervals
    • mainly used for diagnosing narcolepsy or idiopathic hypersomnia
    • overall mean sleep latency <10 minutes is considered clinically significant and patients with narcolepsy have a mean sleep latency <8 minutes


  • Drug and Therapeutics Bulletin (2004); 42(7):52-6.
  • Brown J, Makker KM. An approach to excessive daytime sleepiness in adults. BMJ 2020;368:m1047

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