Narcolepsy

Narcolepsy was first described in 1880 by Jean Baptiste E. Gelineau. It is characterized by excessive day time sleepiness and abnormal rapid eye movement (REM) sleep regulation. Recently it has been reported that the neuropeptide, hypocretin 1 levels in the CSF are at a lower level than in normal subjects. REM sleep represents 20-25% of an adults sleep and occurs in about 5 periods during the night, each following a cycle of NREM sleep. Cataplexy is the most specific symptom and is characterised by partial or complete muscle weakness that can involve the face, neck, legs or total body. The patients are aware of their surroundings but are not able to move. This may present as falls, clumsiness, dropping articles, etc. Cataplexy can be triggered by strong emotions such as laughter, anger, surprise etc.

Sleep paralysis and hypnagogic hallucinations are the other symptoms seen with narcolepsy. Polysomnography is the gold standard for diagnosing obstructive sleep apnoea (OSA). Multiple sleep latency test (MSLT) is used to diagnose narcolepsy. MSLT measures the time required for a subject to fall asleep during 4-5 nap opportunities. The presence of REM sleep during at least 2 such naps is diagnostic of narcolepsy. Prior to performing MSLT, OSA should be excluded by polysomnography. Patients with narcolepsy are known to have an unsually high rate of HLA-DQB1*0602. Narcolepsy is treated using stimulant medication. Methylphenidate, amphetamine, modafinil & pemoline have all been tried.

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Narcolepsy is characterised by cataplexy, sleep paralysis, hypnagogic hallucinations and excessive daytime sleepiness. Over 24 hours, patients with narcolepsy do not sleep more than normal controls, but they are prone to fall asleep throughout the day, often at inappropriate times. Nocturnal apnoea spells are not a feature. Such patients lack hypocretin in the CSF. In patients with narcolepsy, night sleep is often interrupted by repeated awakenings and terrifying dreams.

Kryger MH, Roth T and Dement WC. Principles and Practice of Sleep Medicine
3rd edn. Philadelphia: WB Saunders, 2000: p 676-686