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Narcolepsy

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Overview

Narcolepsy is a chronic condition characterised by excessive sleepiness and falling asleep at irregular times due to the brain failing to regulate sleep and wake patterns. Its aetiology is unknown but it is thought to be involved with reduced orexin (hypocretin) function.

Cataplexy is a sudden and transient loss of muscle tone, usually triggered by strong emotions such as laughter. Cataplexy is very strongly associated with narcolepsy.

Epidemiology

  • Narcolepsy is the second most common cause of disabling daytime sleepiness following obstructive sleep apnoea
  • Age of onset is usually adolescence

Risk Factors

Presentation

Overview

There is a classic tetrad of narcolepsy:

  • Excessive daytime sleepiness
    • Patients may have “sleep attacks” – falling asleep at inappropriate times
    • Patients may have poor memory and concentration
  • Cataplexy
  • Sleep paralysis
  • Hallucinations that occur when:
    • Going to sleep (hypnagogic) or 
    • Waking (hypnopompic)

Cataplexy

  • Cataplexy is a transient loss of muscle tone usually triggered by strong emotions such as laughter.
    • The severity can vary from slackening facial muscles to knees buckling, to collapse with nearly all muscles being affected.

Differential Diagnoses

Obstructive sleep apnoea

  • Patients have periods of no breathing (apnoea), gasp for air, or choke during sleep
  • There is often snoring
  • Patients may be obese/have a large neck circumference etc. 

Investigations

  • Refer patients to sleep disorder service
  • Polysomnogram followed by multiple sleep latency tests (MSLT) + electroencephalograms (EEGs)

Diagnosis

Narcolepsy with cataplexy

  • Excessive sleepiness almost daily for ≥3 months
  • Cataplexy present
  • Confirmation through polysomnography followed by MSLT or CSF hypocretin-1 levels
  • Excessive sleepiness is not better explained by another condition

Narcolepsy without cataplexy

  • Excessive sleepiness almost daily for ≥3 months
  • Confirmation through polysomnography 

Management

  • 1st-line: modafinil during the day and sodium oxybate during the night
  • Consider serotonin-noradrenaline reuptake inhibitors (SNRIs; e.g. venlafaxine), tricyclic antidepressants (TCAs; e.g. clomipramine), or selective serotonin-reuptake inhibitors (SSRIs; e.g. fluoxetine) for cataplexy

Monitoring and Patient Advice

Monitoring

  • Patients are generally followed up every 6 to 12 months to review symptoms and responses to treatment
  • The Epworth sleepiness scale can be used to monitor sleepiness

Patient Advice

  • Patients should be encouraged to improve their sleep hygiene and make appropriate lifestyle changes where possible
  • Patients should not drive or operate heavy machinery while sleepy
  • Patients should avoid alcohol consumption

Complications and Prognosis

Complications

  • Depression
  • Accidents and injuries
  • Obesity and metabolic syndrome

Prognosis

  • Narcolepsy is usually lifelong but can be improved with treatment/retirement

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