Hypersomnias of Central Origin
Narcolepsy
Narcolepsy type 1 features cataplexy and orexin deficiency; type 2 lacks cataplexy and has normal orexin. Symptoms include excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, sleep paralysis, and disrupted nighttime sleep. Diagnosis uses MSLT (mean sleep latency ≤8 min, ≥2 SOREMPs) or CSF orexin ≤110 pg/mL. Treatment: modafinil, stimulants, sodium oxybate (especially for cataplexy), and antidepressants for cataplexy.
Idiopathic hypersomnia
Characterized by excessive sleepiness without cataplexy, with long unrefreshing naps and prolonged sleep. MSLT shows short latency but fewer than two SOREMPs. Treatment is symptomatic with wake-promoting agents.
Kleine-Levin syndrome
Recurrent episodes of hypersomnia, hyperphagia, and behavioral changes, mostly in adolescent males, with normal function between episodes.
Traps
A single SOREMP is insufficient. Sleep deprivation can mimic narcolepsy on MSLT, so confirm adequate sleep first. Cataplexy must be triggered by emotion and preserve consciousness. Do not diagnose narcolepsy type 2 if orexin is low or cataplexy is present.
Rule of thumb: Emotion-triggered loss of muscle tone with preserved consciousness = cataplexy; add sodium oxybate if cataplexy is prominent.