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Introduction

Narcolepsy is a chronic sleep disorder characterized by excessive daytime sleepiness with overwhelming urges to fall asleep suddenly, often at inappropriate times.  It is typically accompanied by cataplexy, sleep paralysis, and hypnopompic and/or hypnagogic hallucinations.  Narcolepsy can significantly impact quality of life and interfere with daily activities.

Epidemiology

Approximately 0.05% of the global population has narcolepsy, with peak onset in patients age 15-25.  Cataplexy is present in approximately 70% of patients.

Pathogenesis

The pathogenesis of narcolepsy involves the loss of hypocretin-producing neurons in the hypothalamus.  Hypocretin-1 (orexin-A) and hypocretin-2 (orexin-B) are neuropeptides that promote wakefulness and inhibit REM (rapid eye movement) sleep.  Hypocretin deficiency shortens the REM latency period, causing an awake individual to rapidly enter REM sleep unexpectedly, a phase where muscle tone is lost.

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