Hypersomnias of Central Origin and Narcolepsy
Narcolepsy
Narcolepsy type 1 features cataplexy and hypocretin deficiency; type 2 lacks cataplexy. Classic tetrad: excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, and sleep paralysis. Diagnosis uses MSLT showing mean sleep latency of 8 minutes or less with 2 or more sleep-onset REM periods, after adequate sleep and prior overnight PSG. CSF hypocretin-1 is low in type 1.
Other central hypersomnias
Idiopathic hypersomnia shows long sleep times and unrefreshing naps without REM dysregulation. Kleine-Levin syndrome features recurrent hypersomnia with cognitive and behavioral changes. Distinguish these from insufficient sleep syndrome, which is common and reversible.
Traps
- MSLT must follow adequate sleep; sleep deprivation causes false-positive REM periods.
- Cataplexy is triggered by emotion, typically laughter.
- Medication effects (REM-suppressing or REM-enhancing drugs) alter MSLT results and require washout.
- Obstructive sleep apnea can mimic narcolepsy; treat and reassess.
Rule of thumb
Two or more sleep-onset REM periods plus short mean sleep latency on MSLT supports narcolepsy; confirm sleep was adequate first.