Épidémiologie des hypersomnies d'origine centrale

Epidemiology is the study of the distribution of diseases among populations, of risk factors and of targets for preventive medicine. The hypersomnias of central origin include mainly narcolepsy with and without cataplexy, idiopathic hypersomnia with and without long sleep time and recurrent hypersomnia with two conditions, Kleine-Levin syndrome and menstrual related hypersomnia. Narcolepsy with cataplexy has a prevalence of 20 to 40 per 100 000 with two notable exceptions: a prevalence greater than 100 for 100 000 in the Japanese population and a prevalence of less than 1 for 100 000 in the Israeli population, possibly in relation with a high percentage of HLA-DR2 positive subjects in the Japanese population and a very low percentage of them in the Israeli population. The prevalence of narcolepsy without cataplexy is not well defined. The incidence of narcolepsy with and without cataplexy is between 0.60 and 1.40 per year and for 100 000. Narcolepsy depends on genetic and environmental factors. Present studies underscore important roles for certain genes and implicate additional genes. Main environmental factors might be infectious. Preventive measures against the condition do not exist yet. The prevalence of idiopathic hypersomnia, with and without long sleep time is still unknown. Genetic factors are also unknown in spite of a high rate of family cases. There is no preventive measure up to now. Kleine-Levin syndrome and menstruation-linked hypersomnia are exceptional conditions, the prevalence of which we do not know. Genetic basis of the condition is currently unveiling while environmental factors have been known for long. A partial prevention of relapses is available, mainly based on lithium therapy.