351 Discussion Figure 2. Previous, current and proposed diagnostic classification of central disorders of hypersomnolence in absence of cataplexy. The lines and arrows represent the general direction in which individuals are regrouped based on the changing diagnostic criteria. The people with idiopathic hypersomnia with long sleep time (ICSD-2) would generally be grouped in the idiopathic hypersomnia group of the European experts position paper (dotted line). EDS = Excessive daytime sleepiness; ICSD-2 = Second edition of the International Classification of Sleep Disorders; ICSD-3 = Third edition of the International Classification of Sleep Disorders; ICSD-3TR = Third edition of the International Classification of Sleep Disorders – Text Revision; IH = Idiopathic hypersomnia; MSLT = Multi sleep latency test; NT1 = Narcolepsy type 1; NT2 = Narcolepsy type 2; PSG = Polysomnography; SOREMPs = Sleep-onset rapid eye movement periods. Roughly 10% of individuals with narcolepsy type 2 eventually develop cataplexy [50, 192, 193]. It is currently difficult to identify these individuals in early disease stages when cataplexy is not yet present and hypocretin concentrations have not been determined. Future research should focus on identifying better predictors for these individuals [50]. The remaining majority of central disorders of hypersomnolence with normal sleep time without cataplexy were grouped in a single cluster as presented in Chapter 9, with a notable absence of sleep drunkenness and without weekend-week sleep length difference. This cluster resembles the “idiopathic excessive sleepiness” group of the position paper by European experts [28], in which daytime manifestations of excessive daytime sleepiness persisted for at least three months, complemented with confirmation by polysomnography and MSLT mean sleep latency below eight minutes (or 12 minutes in case of a probable diagnostic certainty). These individuals should also not meet European expert criteria for narcolepsy or idiopathic hypersomnia. Similar diagnostic restructuring was recently proposed by a group of global experts on hypersomnolence disorders but this position paper provided fewer diagnostic directions [27]. This group of global experts suggested to introduce the name “narcolepsy spectrum disorder” for the individuals with excessive daytime sleepiness with normal sleep time without cataplexy. As with the current diagnostic names, using the term narcolepsy would continue to create confusion about its specificity for hypocretin deficiency 11
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