ICSD Criteria for Narcolepsy
The International Classification of Sleep Disorders (ICSD-3) divides narcolepsy into Type 1 and Type 2, with Type 1 requiring either cataplexy or documented CSF hypocretin deficiency, while Type 2 requires absence of cataplexy with normal or undocumented CSF hypocretin levels. 1
ICSD-3 Diagnostic Criteria
Narcolepsy Type 1
All of the following must be present 1:
- Excessive daytime sleepiness (EDS) occurring daily for at least 3 months 2
- PLUS one of the following:
- Definite history of cataplexy (episodes of muscle weakness triggered by emotion, typically laughter or anger, manifesting as leg/arm weakness, knee buckling, or dropping objects) 2, 3
- CSF hypocretin-1 deficiency (≤110 pg/mL or <1/3 of mean normal values) 4, 1
- Positive objective sleep testing: Mean sleep latency ≤8 minutes on MSLT with ≥2 sleep-onset REM periods (SOREMPs), where a SOREMP on preceding nocturnal PSG can count as one of the required SOREMPs 1
Narcolepsy Type 2
All of the following must be present 1:
- Excessive daytime sleepiness occurring daily for at least 3 months 2
- Positive MSLT findings: Mean sleep latency ≤8 minutes with ≥2 SOREMPs (a SOREMP on PSG within 15 minutes of sleep onset may substitute for one MSLT SOREMP) 1
- Cataplexy is absent 1
- CSF hypocretin-1 levels are either normal (>110 pg/mL) or not measured 1
- Symptoms are not better explained by other sleep disorders, medical conditions, medications, or substance use 1
Key Diagnostic Features
Cataplexy Characteristics
- Consciousness is preserved throughout the episode (patients can recall everything that happened) 3
- Triggered by strong emotions, particularly laughter 3
- No post-ictal confusion, distinguishing it from seizures 3
- Pathognomonic for narcolepsy when present with daytime sleepiness 3
Associated REM Sleep Phenomena
Additional symptoms that may be present but are not required for diagnosis 2, 5:
- Hypnagogic/hypnopompic hallucinations (visual hallucinations at sleep onset or upon awakening) 2
- Sleep paralysis (immobility occurring at sleep onset or upon awakening) 2
- Disrupted nocturnal sleep 6
- Automatic behaviors (episodes during sleepiness not subsequently remembered) 2
Objective Testing Requirements
Multiple Sleep Latency Test (MSLT)
- Must be preceded by overnight polysomnography to rule out other sleep disorders 4, 5
- Mean sleep latency ≤8 minutes across 4-5 nap opportunities 1, 5
- ≥2 sleep-onset REM periods (REM sleep occurring within 15 minutes of sleep onset) 1
- A SOREMP on the preceding PSG (REM latency ≤15 minutes) can count as one of the required SOREMPs 1
CSF Hypocretin-1 Testing
- Type 1 narcolepsy results from degeneration of hypothalamic neurons producing orexin/hypocretin 4
- Diagnostic threshold: ≤110 pg/mL or <1/3 of mean normal control values 1
- Not routinely recommended in Prader-Willi syndrome despite narcolepsy-like features, as levels are typically not as low as in narcolepsy type 1 4
Important Clinical Caveats
Diagnostic Pitfalls
- Cataplexy presentation varies significantly in children, including profound facial hypotonia, tongue/perioral muscle movements, and hyperkinetic movements that may resemble seizures but occur without loss of consciousness 3
- Cataplexy may be ambiguous or absent at initial presentation, with only 15-30% of narcoleptic individuals ever diagnosed, and nearly half first presenting after age 40 5
- Long delays between symptom onset and diagnosis are common due to mild disease severity or misdiagnoses 5
When to Refer to Sleep Specialist
Refer to a sleep specialist when narcolepsy or idiopathic hypersomnia is suspected or when the cause of sleepiness is unknown 7. Sleep specialists have expertise to:
- Differentiate narcolepsy from other causes of excessive sleepiness (obstructive sleep apnea, idiopathic hypersomnia, medication-induced hypersomnia) 7
- Perform and interpret specialized testing (MSLT, PSG, possible CSF analysis) 7
- Manage complex pharmacological treatment including modafinil, sodium oxybate, and antidepressants 7