350 Chapter 11 Central disorders of hypersomnolence with long sleep time without cataplexy There is consensus among most experts on the presence of a subgroup of individuals with increased daily sleep need [27, 28]. These individuals were classified in a separate diagnostic entity in the second edition of the International Classification of Sleep Disorders (ICSD-2) (Figure 2): idiopathic hypersomnia with long sleep time [7]. Long sleep time was defined as more than 11 hours, a threshold chosen with limited scientific support. In the following ICSD-3 [8] and the recent ICSD-3 Text Revision [9], these individuals were incorporated in the overarching idiopathic hypersomnia group, together with people without long sleep time (MSLT mean sleep latency below eight minutes in absence of multiple SOREMPs). In our results presented in Chapter 9, one of the clusters of people without cataplexy had longer sleep time during weekend days compared to weekdays, a variable that quantifies unfulfilled sleep need. People with increased sleep need often cannot meet their longer sleep requirements during the week due to work or social commitments, while weekends allow more unrestricted sleep. Within this same cluster we also found almost uniform presence of sleep drunkenness with frequent subjective difficulty awakening. A recent position paper by many European experts (led by Prof. Dr. Lammers who also was the senior author on our clustering manuscript) similarly suggested the introduction of the “excessive need for sleep” phenotype as the main criterion for the diagnosis idiopathic hypersomnia [28] (Figure 2). Excessive need for sleep would be defined as the combination of an acquired increased sleep need, verified by two-week actigraphy and 24-hour polysomnography, with daytime manifestations of excessive daytime sleepiness and/or sleep drunkenness. Our results shown in Chapter 9 provide the data-driven evidence for new symptom-centred criteria in which weekend-week sleep length difference, sleep drunkenness and subjective difficulty awakening should be considered. Central disorders of hypersomnolence without long sleep time without cataplexy There is less consensus on optimal subgrouping of individuals with excessive daytime sleepiness, normal sleep durations and absence of cataplexy. Current ICSD-3 Text Revision criteria (similar to the ICSD-3) distinguish narcolepsy type 2 and idiopathic hypersomnia solely based on presence of multiple SOREMPs during the MSLT (Figure 2) [8, 9]. The poor test-retest reliability [34, 35] of the MSLT and our results in Chapter 9 urge reconsidering this differentiation.
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