In comparison with narcolepsy, which is characterized by well-defined clinical, polysomnographic, and immunogenetic features, idiopathic hypersomnia is not well delineated and its history is much more recent.

In 1966, Dement et al<sup>10Dement W.C., Rechtschaffen A., Gulevich G. The nature of the narcoleptic sleep attack Neurology 1966 ;  16 : 18-33

Cliccare qui per andare alla sezione Riferimenti</sup> proposed that subjects with excessive daytime sleepiness but no cataplexy, sleep paralysis, or sleep-onset rapid eye movement (REM) periods should not be considered narcoleptic. Subsequently, Berti-Ceroni et al<sup>6Berti-Ceroni G., Coccagna G., Gambi D., e al. Considerationi clinico poligrafiche sull narcolessia essenziole a somno lento Sist Nerv 1967 ;  19 : 81-89

Cliccare qui per andare alla sezione Riferimenti</sup> and Passouant et al<sup>22Passouant P., Popoviciu L., Velok G., e al. Etude polygraphique des narcolepsies au cours du nycthémère Rev Neurol (Paris) 1968 ;  118 : 431-441

Cliccare qui per andare alla sezione Riferimenti</sup> described narcolepsy with non–rapid eye movement (NREM) sleep episodes. The clinical picture was still vague, however, and it is very likely that among the subjects under consideration were subjects with other sleep disorders, including respiratory disorders associated with sleep. In 1972, Roth et al<sup>28Roth B., Nevsimalova S., Rechtschaffen A. Hypersomnia with sleep drunkenness Arch Gen Psychiatry 1972 ;  26 : 456-462

Cliccare qui per andare alla sezione Riferimenti</sup> circumscribed the limits of the condition in describing a type of “hypersomnia with sleep drunkenness,” which consisted of difficulty in coming to complete wakefulness accompanied by confusion, disorientation, poor motor coordination, and slowness associated with deep and prolonged sleep. Four years later, the same group proposed a classification of hypersomnolent conditions, which included narcolepsy, hypersomnia, and the subwakefulness syndrome.<sup>25Roth B. Functional hypersomnia Narcolepsy New York: Spectrum (1976).  333

Cliccare qui per andare alla sezione Riferimenti</sup> Hypersomnia was considered either symptomatic or functional, with the functional form subdivided into a functional hypersomnia with a short cycle and a functional hypersomnia with a long cycle (periodic hypersomnia). Functional hypersomnia with a short cycle was further subdivided into idiopathic hypersomnia and neurotic hypersomnia. Finally, idiopathic hypersomnia was considered either monosymptomatic, manifested only by excessive daytime sleepiness and not by abnormal awakening, or polysymptomatic, characterized by excessive daytime sleepiness, nocturnal sleep of abnormally long duration, and signs of “sleep drunkenness” on awakening.

According to the International Classification of Sleep Disorders (ICSD),<sup>3American Sleep Disorders Association ICSD—International Classification of Sleep Disorders: Diagnostic and Coding Manual. Diagnostic Classification Steering Committee, Thorpy MJ (Chairman) Rochester, MN: American Sleep Disorders Association (1990).  285

Cliccare qui per andare alla sezione Riferimenti</sup> idiopathic hypersomnia is “a disorder of presumed central nervous system cause that is associated with a normal or prolonged major episode and excessive sleepiness consisting of prolonged (1–2 hours) sleep episodes of NREM sleep.” Clearly, the ICSD definition merges Roth's monosymptomatic and polysymptomatic forms by indicating that some patients report great difficulty waking up and experience disorientation after awakening.

Finally, based on a retrospective review of clinical and polygraphic findings and questionnaire results in groups of subjects with narcolepsy, narcolepsy without cataplexy, idiopathic hypersomnia, insufficient sleep syndrome, mild sleep apnea, and excessive daytime sleepiness not otherwise specified, Aldrich<sup>2Aldrich M.S. The clinical spectrum of narcolepsy and idiopathic hypersomnia Neurology 1996 ;  46 : 393-401

Cliccare qui per andare alla sezione Riferimenti</sup> suggests that the syndrome of idiopathic hypersomnia is a heterogeneous syndrome. He also reports that relatively few patients have the polysymptomatic form of idiopathic hypersomnia described by Roth<sup>25Roth B. Functional hypersomnia Narcolepsy New York: Spectrum (1976).  333

Cliccare qui per andare alla sezione Riferimenti</sup> and that other subjects experience prolonged sleep without sleep drunkenness, excessive daytime sleepiness without prolonged sleep hours, a clinical syndrome with sleep paralysis, or sleep-related hallucinations clinically indistinguishable from narcolepsy without cataplexy but without REM sleep abnormalities.