Sleep attack
Orexin (hypocretin) deficiency
HallmarkCataplexy (emotion-triggered)
DiagnosticCSF hypocretin-1 ≤110 pg/mL
MSLT≤8 min + ≥2 SOREMPs
HLADQB1*06:02 assoc — NOT diagnostic
Cataplexy triggered by laughter? Low CSF hypocretin clinches narcolepsy type 1 — no MSLT needed.
Narcolepsy type 1 vs idiopathic hypersomnia
| Narcolepsy type 1 | Idiopathic hypersomnia | |
|---|---|---|
| Cataplexy | Present (pathognomonic) | Absent |
| CSF hypocretin | ≤110 pg/mL (diagnostic) | Normal |
| MSLT latency | ≤8 min | ≤8 min |
| SOREMPs | ≥2 (PSG SOREMP counts) | <2 |
◆ Signature clue
Cataplexy + CSF hypocretin-1 ≤110 pg/mL → narcolepsy type 1 (diagnostic even without MSLT). Both NT1 and IH have MSLT ≤8 min — the SOREMPs (≥2 vs <2) split them.
Diagnosis
Still requires the clinical syndrome — chronic EDS with insufficient sleep, OSA, and medication effects excluded first; hypocretin is not the first test for every sleepy patient. HLA-DQB1*06:02 is associated but NOT diagnostic (12–25% of the population carry it).
Management
Oxybate & pitolisant treat both EDS and cataplexy; modafinil / solriamfetol are EDS-only. Antidepressants (SNRIs/TCAs) off-label for cataplexy.