[Physiopathology of idiopathic hypersomnia. Current studies and new orientations]

In 1976 Bedrich Roth coined the term "idiopathic hypersomnia" and described two forms of the disease, one monosymptomatic, manifested only by excessive daytime sleepiness, and one polysymptomatic, characterized by excessive daytime sleepiness, nocturnal sleep of abnormally long duration and signs of "sleep drunkenness" on awakening. In comparison with that of narcolepsy, the pathophysiology of idiopathic hypersomnia remains poorly known. There are two main reasons for that: the absence of clinical and polysomnographic criteria pathognomonic or at least characteristic of the condition, as the cataplexies and the sleep onset REM periods of narcolepsy, and also the absence of a natural animal model comparable with the canine model of narcolepsy. The first investigations have stressed the frequent familial pattern of idiopathic hypersomnia. Later on biochemical assays have been performed in the CSF with results in favour of a dysfunction of noradrenergic systems. In the light of the two process model of sleep regulation in which sleep propensity is determined by a homeostatic process S and a circadian process C and of the later three-process model of regulation in which sleepiness/alertness are simulated by the combined action of a homeostatic process, a circadian process and sleep inertia, we suggest that idiopathic hypersomnia is not a pathological entity in itself, but rather the consequence of chronic sleep deprivation in very long sleepers.