[Narcolepsy].

First described as a separate entity by Gelineau in 1880 and later considered as a symptom, narcolepsy has eventually been recognized as a disease on clinical and polygraphic grounds. Its prevalence stays between 0.04 and 0.06 percent. Age at onset varies from 5 to 50 with a peak in the second decade. Clinical symptoms include excessive daytime somnolence, overwhelming daytime sleep episodes, attacks of cataplexy, hypnagogic hallucinations, sleep paralysis and disturbed nocturnal sleep; sleep onset REM episodes are the main polygraphic feature. Natural history varies with the different symptoms. Excessive daytime somnolence never subsides completely. Cataplexy may disappear spontaneously. Hypnagogic hallucinations and sleep paralysis are not present in all patients and tend to be more transitory. A positive diagnosis of narcolepsy requires a minimum of one major symptom, daytime sleep episodes or cataplexy, together with documented sleep onset REM episodes. Prolonged polygraphic recordings or multiple sleep latency test are of special interest in difficult cases. Clinical variants can be grouped under three headings, incomplete, symptomatic and associated narcolepsies. The etiology of narcolepsy is not well understood. However the discovery of natural animal models of narcolepsy, mainly dogs, has prompted genetic, pharmacological and biochemical studies. The breeding of narcoleptic canine colonies has led to the evidence of a possible autosomal recessive model of inheritance in some species. Pharmacological and neurochemical analysis has shown an imbalance between monoaminergic and cholinergic mechanism. In man, extensive family studies suggest either a two-threshold multifactorial model of inheritance or a dominant mode of inheritance and immunologic studies have recently shown a strong association between HLA-DR2 and narcolepsy. Assays of CSF biogenic amines suggest a decreased bioavailability of dopamine to explain sleepiness and an imbalance between monoamines and acetylcholine to explain cataplexy. A disturbance of circadian rhythms has not been evidenced in narcoleptics. Treatment is still purely symptomatic. Amphetamines and tricyclic antidepressants have been extensively used. However they are not free of side-effects hence the need for alternative treatments.