TABLE 2

Key clinical and diagnostic features of narcolepsy and other central disorders of hypersomnolence

Clinical features in addition to EDS to help differentiateDistinguishing features on diagnostic testing
Type 1 narcolepsyCataplexy (sudden loss of muscle tone in response to emotion) is pathognomonic
Hypnagogic hallucinations and sleep paralysis in 50–60% of patients
Disturbed nocturnal sleep
Actigraphy: >6 h·night−1
PSG: SOREMP suggestive of diagnosis
Fragmented nocturnal sleep
± Increased EMG tone during REM
MSLT: short sleep latency ≤8 min and ≥2 SOREMPs
CSF orexin levels: low ≤110 pg·mL−1 or <1/3 of mean values in normal subjects; often undetectable
Type 2 narcolepsyAs type 1 narcolepsy but no cataplexyActigraphy: >6 h·night−1
MSLT: short sleep latency ≤8 min and ≥2 SOREMPs
CSF orexin levels: normal or intermediate >110 pg·mL−1 or >1/3 of mean values in normal subjects
Idiopathic hypersomniaSleep drunkenness/sleep inertia on awakening
Non-refreshing naps
± Long sleep times
Actigraphy: regular or long sleep times (diagnosis can be made if average 24-h sleep time >660 min over ≥7 days)
PSG: may show high sleep efficiency, increased slow-wave sleep
MSLT: short sleep latency ≤8 min and <2 SOREMPs
Kleine–Levin syndromeEpisodes of recurrent hypersomnia (1–4 weeks) with neuropsychiatric features
Asymptomatic between episodes
PSG normal between events
EEG may show slowing during episode
Hypersomnia due to a medical disorderEDS with associated features of a particular condition such as Parkinson disease, stroke, etc.
Hypersomnia associated with a psychiatric disorderEDS in patients with a psychiatric condition
Atypical depression may have a similar phenotype to idiopathic hypersomnia
MSLT: sleep latency may be normal or short, rarely SOREMP
Hypersomnia due to a medication or substanceEDS related to medication: careful review of medication history and consideration of urine toxicologyMSLT may show short sleep latency, confounding diagnosis if medication effect not suspected
Urine toxicology as part of MSLT protocol is helpful
Insufficient sleep syndromeChronic EDS due to sleep deprivationActigraphy: irregular/insufficent sleep times
PSG: reduced sleep latency, high sleep efficiency, increased slow-wave sleep
MSLT: sleep latency short, occasionally SOREMP

Data from the International Classification of Sleep Disorders, third edition [86]. EDS: excessive daytime sleepiness; PSG: polysomnography; SOREMP: sleep-onset rapid eye movement period; EMG: electromyogram; REM: rapid eye movement; MSLT: multiple sleep latency test; CSF: cerebrospinal fluid; EEG: electroencephalogram.