Narcolepsy and Sleep Disorders
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Direct answer
Narcolepsy is a chronic disorder of sleep-wake regulation characterised by excessive daytime sleepiness, and the classic form with cataplexy reflects loss of hypocretin (orexin) neurons in the hypothalamus. Narcolepsy type 1 with cataplexy has low or undetectable hypocretin-1 in cerebrospinal fluid, whereas type 2 lacks cataplexy and usually has normal levels. Diagnosis rests on polysomnography to exclude sleep apnoea, followed by multiple sleep latency testing, and treatment combines a wakefulness-promoting drug with sodium oxybate or another agent for cataplexy.
What you must remember
- Narcolepsy tetrad: excessive daytime sleepiness, cataplexy, sleep paralysis and hypnagogic hallucinations; cataplexy is the most specific symptom.
- Cataplexy: brief loss of muscle tone triggered by strong emotion such as laughter, with consciousness preserved.
- HLA association: HLA-DQB1*06:02 is strongly linked to type 1 narcolepsy, and a negative result argues against it, though it is not diagnostic.
- Multiple sleep latency test: mean sleep latency of 8 minutes or less with two or more sleep-onset REM periods supports narcolepsy.
- REM sleep behaviour disorder: loss of REM atonia with dream enactment and violent movements, often preceding Parkinson disease, dementia with Lewy bodies or multiple system atrophy by years.
- Treatment: modafinil or armodafinil for sleepiness, sodium oxybate for cataplexy and sleepiness, and venlafaxine as an option for cataplexy; driving advice is essential.
A worked case: the student who collapses when he laughs
A 22-year-old engineering student falls asleep in lectures, and when his friends make him laugh his knees give way while he remains fully aware. He also reports sleep paralysis on waking.
- Exclude apnoea first: Polysomnography comes first, to exclude obstructive apnoea and other sleep disorders that could shorten sleep latency.
- Measure sleep latency: The multiple sleep latency test then shows a mean latency of four minutes with three sleep-onset REM periods, and HLA-DQB1*06:02 is positive.
- Confirm with CSF: CSF hypocretin-1 is markedly low, confirming narcolepsy type 1.
- Treat and counsel: Treatment combines modafinil with sodium oxybate for cataplexy. Counselling covers driving, workplace safety and avoiding alcohol with oxybate.
- Contrast REM sleep behaviour disorder: A 68-year-old man who punches and shouts during sleep and has since developed parkinsonism has REM sleep behaviour disorder that predates the motor features. Low-dose clonazepam or melatonin is used, bedroom safety is arranged, and the patient is followed for a synucleinopathy.
- Protect the bed partner: Counselling the bed partner is part of the plan, since injury during dream enactment is often what brings the patient to clinic.
Where the examiner sets the trap
Four traps recur in examiner questions.
- Trap: treating sleepiness in an obese, snoring patient as narcolepsy Correct: this is obstructive sleep apnoea until proved otherwise, and an apnoea-hypopnoea index of 5 or more per hour with symptoms establishes it, with CPAP as the treatment rather than a stimulant.
- Trap: confusing cataplexy with seizures or syncope Correct: cataplexy is emotionally triggered and preserves consciousness.
- Trap: forgetting REM sleep behaviour disorder when the history is dream enactment alone Correct: it is an early warning of neurodegeneration, and candidates often miss it.
- Trap: not knowing why polysomnography comes first Correct: the viva favourite asks why polysomnography precedes the multiple sleep latency test, and the answer is that apnoea would falsely shorten latency.
Frequently asked questions
Which test best confirms narcolepsy type 1 with cataplexy?
Low or undetectable hypocretin-1 in cerebrospinal fluid is the most specific test for narcolepsy type 1 with cataplexy. Polysomnography and multiple sleep latency testing document the sleepiness, while HLA-DQB1*06:02 positivity offers supportive evidence.
What is the first-line treatment for REM sleep behaviour disorder?
Low-dose clonazepam is the classic first-line drug for REM sleep behaviour disorder, and melatonin is commonly used as an alternative. Bedroom safety measures are essential, and the patient should be assessed for an underlying synucleinopathy such as Parkinson disease.
How is cataplexy different from a seizure or syncope?
Cataplexy is a brief loss of muscle tone triggered by strong emotions such as laughter, with consciousness preserved, whereas seizures and syncope involve loss of awareness. Sodium oxybate or venlafaxine treats cataplexy specifically, which is a further reason to identify it correctly.
Why is polysomnography done before a multiple sleep latency test?
Polysomnography excludes obstructive sleep apnoea and other causes of daytime sleepiness that would falsely shorten sleep latency. Only after that does the multiple sleep latency test show whether sleep onset is short enough to support narcolepsy.