OBSOLETE: Idiopathic hypersomnia without long sleep time

Idiopathic hypersomnia without long sleep time was a diagnostic subtype of idiopathic hypersomnia (IH) that has since been rendered obsolete in current classification systems. This category was previously used to describe patients who experienced excessive daytime sleepiness (EDS) and difficulty maintaining wakefulness despite having a normal or near-normal nocturnal sleep duration (typically less than 10 hours). Patients presented with constant, overwhelming drowsiness and an irresistible need to nap during the day, yet their naps were often unrefreshing. Unlike the subtype with long sleep time, these individuals did not exhibit prolonged nighttime sleep episodes or severe sleep inertia (sleep drunkenness), though some overlap existed. This condition primarily affects the central nervous system, specifically the brain's sleep-wake regulatory mechanisms. The underlying cause remains unknown, and no specific biomarker or genetic basis has been identified. The distinction between idiopathic hypersomnia with and without long sleep time was previously recognized in the International Classification of Sleep Disorders (ICSD-2) but was merged into a single entity — idiopathic hypersomnia — in the ICSD-3 (2014), as the clinical distinction was not consistently supported by evidence. Orphanet code 228318 reflects this now-obsolete classification. Treatment approaches for idiopathic hypersomnia, regardless of former subtype, include wake-promoting agents such as modafinil, pitolisant, and sometimes stimulants like methylphenidate or amphetamine derivatives. More recently, lower-sodium oxybate (calcium, magnesium, potassium, and sodium oxybates) has been approved for the treatment of idiopathic hypersomnia. Management remains largely symptomatic, as no curative therapy exists. Good sleep hygiene and scheduled napping may provide some benefit, though responses vary among patients.

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