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Idiopathic hypersomnia is a sleep disorder classified in two forms: idiopathic hypersomnia with long sleep time and idiopathic hypersomnia without long sleep time.
ORPHA:33208Classification level: Disorder
- Primary hypersomnia
- Prevalence: 1-5 / 10 000
- Inheritance: Unknown
- Age of onset: All ages
- ICD-10: F51.1
- OMIM: -
- UMLS: C0751757
- MeSH: -
- GARD: 8737
- MedDRA: -
The prevalence is unknown but has been estimated at 1/10,000 - 1/25,000 for the first form and 1/11,000 to 1/100,000 for the second one. Both forms start before the age of 25 years old and affect both sexes equally.
Idiopathic hypersomnia with long sleep time is characterized by a prolonged (more than 10 hours) nocturnal sleep of good quality, more or less constant excessive day-time sleepiness with prolonged unrefreshing sleep episodes, and difficult awakening with sleep inertia or drunkenness. Idiopathic hypersomnia without long sleep time is characterized by isolated excessive diurnal somnolence of over 3 months, with irresistible and more or less refreshing diurnal naps. Nocturnal sleep is normal or slightly prolonged but lasts less than 10 hours, and quality of awakening is often normal. Idiopathic hypersomnia is never associated with cataplexy.
Etiology is unknown. There is no association with any particular HLA marker or with a decrease in the orexin/hypocretin levels.
Diagnosis is complex and must exclude other causes of sleepiness and recognize the excess of sleep. Definitive diagnosis is based on polysomnography completed with multiple sleep latency tests (MSLT). These tests reveal a sleep of good quality and reveal a mean sleep latency of less than 8 min with a maximum of one episode of paradoxical sleep. In case of idiopathic hypersomnia with long sleep time, a 24h-36h continuous recording is made after the MSLT that shows a nocturnal sleep episode of over 10 hours with a daytime nap of more than an hour.
Clinical examination (based more or less on a sleep diary or on actimetry) eliminates chronic insufficient sleep syndrome. Sleep recordings exclude narcolepsy, rhythm disorders or fragmented night sleep due to motor or respiratory events. A psychological examination excludes hypersomnia of psychiatric origin. Finally, neuro-radiological tests, which are rarely performed, exclude cerebral lesions.
Management and treatment
Treatment is based on stimulants such as modafinil, which is the first-line treatment due to its better risk/benefit ratio. Other stimulant drugs are methylphenidate and amphetamines. Active in cases of daytime sleepiness, these drugs have little effect on sleep drunkness observed in idiopathic hypersomnia with long sleep time.
The disease has a negative social and professional impact. Its evolution is often stable in severity, with some spontaneous improvements described.
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