drowsiness (irresistible daytime)

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Despite being first described in 1880 by Gelineau, narcolepsy remains an underdiagnosed cause of excessive daytime sleepiness.

The typical episodes of irresistable sleep are due to abnormal intrusion of REM sleep into wakefullness.

  • in narcolepsy there is a disruption in the usual patterns of non-rapid-eye-movement (NREM) sleep and rapid-eye-movement (REM), or 'dreaming', sleep. As a consequence, this causes difficulty in staying asleep and in staying awake and bouts of irresistible daytime sleepiness under unusual circumstances (e.g. while eating or talking) (1)
  • other characteristic features (these represent intrusions of REM sleep into wakefulness), include:
    • cataplexy
      • a sudden loss of muscle tone - this feature is provoked by emotional stimuli and which can make the person fall
      • individuals may have symptoms of cataplexy, in which there is sudden transient loss of muscle tone, typically in response to emotional stimulus
      • (2)
    • sleep paralysis
      • unpleasant generalised paralysis - this occurs just before, or while, falling asleep or on waking
    • vivid hallucinations on falling asleep (hypnagogic) or on waking (hypnopompic)

Narcolepsy has a strong genetic aetiology.

  • is a primary neurological condition affecting hypocretin producing neurones in the hypothalamus
  • lack of the neurotransmitters hypocretin 1 and 2 (also known as orexin A and B) leads to failure to control sleep and wakefulness

Diagnosis of narcolepsy requires assessment in a specialist centre with facilities for multiple sleep latency test (MSLT) and polysomnography and treatment is based on lifestyle modification and the use of wakefulness promoting medications such as modafinil and sodium oxybutate

There are effective pharmacological treatments.

There are estimated to be around 1 in 3,000 people with narcolepsy, which typically starts in adolescence or early adult life (1)

  • the prevalence varies among different populations, being more common in Japan (around 0.16% of the population) and less common among Ashkenazy Jews (around 0.002%) (2)

Reference:

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

Last edited 06/2020 and last reviewed 12/2020

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