Central Disorders of Hypersomnolence
Categories
Narcolepsy type 1 (NT1) requires excessive daytime sleepiness plus cataplexy and/or cerebrospinal fluid hypocretin-1 ≤110 pg/mL; narcolepsy type 2 (NT2) has sleepiness and abnormal MSLT findings without cataplexy or low hypocretin. Idiopathic hypersomnia (IH) causes sleepiness without the REM dysregulation of narcolepsy. Kleine-Levin syndrome is recurrent hypersomnia with cognitive and behavioral changes. Secondary causes include insufficient sleep syndrome, obstructive sleep apnea, circadian misalignment, depression, and medication effects.
Testing
MSLT after adequate sleep (usually ≥6 hours by history or actigraphy for about a week) and a preceding nocturnal PSG: mean sleep latency ≤8 minutes with ≥2 sleep-onset REM periods (SOREMPs), one of which may be from the preceding PSG, supports narcolepsy. A SOREMP on the PSG alone is not diagnostic. CSF hypocretin is not needed when cataplexy is unambiguous. Note that MSLT results can be confounded by insufficient sleep, shift work, REM-suppressing or REM-rebounding drugs, and untreated OSA.
Clinical features and treatment
Cataplexy (sudden loss of muscle tone triggered by emotion, with preserved consciousness), hypnagogic hallucinations, sleep paralysis, and fragmented nocturnal sleep define the narcolepsy tetrad. Treatment: wake-promoting agents (modafinil/armodafinil, solriamfetol, pitolisant) and sodium oxybate (also reduces cataplexy); stimulants are used as needed. IH is treated with wake-promoting agents; response is variable.
Traps
Low MSLT latency alone (without ≥2 SOREMPs) does not diagnose narcolepsy; insufficient sleep is the most common mimic.