Narcolepsy Type 1: Caused by the loss of hypocretin (orexin)-producing neurons in the lateral hypothalamus. This is thought to be an autoimmune process, often linked to the HLA-DQB1 06:02 haplotype. The lack of hypocretin leads to instability in the sleep-wake cycle, causing elements of REM sleep to intrude into wakefulness.
Narcolepsy Type 2: The exact cause is less clear, but hypocretin levels are typically normal. It may involve less severe neuronal loss or issues with hypocretin receptor signaling.
Excessive Daytime Sleepiness (EDS): Irresistible “sleep attacks” and persistent drowsiness despite adequate nighttime sleep. Naps are often short and refreshing.
Cataplexy: Pathognomonic for Type 1. It is a sudden, brief loss of muscle tone triggered by strong emotions like laughter, excitement, or anger. Awareness is preserved.
Hypnagogic/Hypnopompic Hallucinations: Vivid, dream-like hallucinations that occur while falling asleep (hypnagogic) or waking up (hypnopompic).
Sleep Paralysis: Inability to move or speak for a few seconds to minutes upon awakening or falling asleep.
Onset is typically in adolescence or young adulthood (ages 15-25).
Diagnostics
The gold standard for diagnosis involves a combination of clinical evaluation, a nocturnal polysomnography (PSG) followed by a Multiple Sleep Latency Test (MSLT).
MSLT findings: Mean sleep latency of ≤ 8 minutes and the presence of ≥ 2 sleep-onset REM periods (SOREMPs). A SOREMP is entering REM sleep within 15 minutes of sleep onset.
CSF analysis: Low levels of hypocretin-1 (< 110 pg/mL) are diagnostic for Narcolepsy Type 1.
Treatment
General measures
Optimize sleep hygiene.
Ensure regular sleep periods during the night.
Avoid substances that disturb the sleep-wake cycle (e.g., alcohol, antipsychotics, opiates).
Consider scheduled naps throughout the day to reduce the urge to sleep.