Idiopathic Hypersomnia

Idiopathic hypersomnia is clinically similar to narcolepsy in that daytime sleepiness occurs despite adequate amounts of apparently normal sleep at night, but cataplexy does not occur and there is no association with specific HLAs. The pathogenesis is unknown. Circulating somnogenic factors or focal lesions that affect systems involved in sleep-wake regulation may play a role in some cases. Idiopathic hypersomnia is less common than narcolepsy by a ratio of about 1:10. Recent viral illness may be a risk factor.

Symptoms often develop gradually during adolescence or young adulthood. There appear to be at least two types of idiopathic hypersomnia, but many patients have mixed features. With the classic type, patients complain of an increased need for sleep, difficulty awakening in the morning, and sleep drunkenness with disorientation and confusion in the morning.y Daytime naps are long and unrefreshing, and patients may sleep as much as 14 to 18 hours during the day and night. With the second type, daytime sleepiness is sometimes irresistible, similar to narcolepsy, but short naps are usually refreshing.

Other diagnostic considerations in patients who complain of long periods of unrefreshing sleep include atypical depression and chronic fatigue syndrome. In both of these disorders, patients often spend many hours in bed, but actual sleep time is increased only mildly or not at all. Idiopathic hypersomnia is usually considered in a patient who complains of sleepiness and has no apparent cause for sleepiness based on the clinical history and a nocturnal polysomnogram. For such patients, the differential diagnosis includes narcolepsy, upper airway resistance syndrome, insufficient sleep syndrome, and obstructive sleep apnea that occurs during some nights but not others. The diagnosis of idiopathic hypersomnia is not easy because it requires ruling out all other causes to the extent possible.

Evaluation should include one or more nights of polysomnography, MSLT, psychiatric assessment, and a trial of increased sleep. The upper airway resistance syndrome may be difficult to detect on polysomnography unless airway resistance is assessed with monitoring of endoesophageal pressure during polysomnography.^ Patients with narcolepsy may not have REM sleep abnormalities on an initial MSLT. Atypical depression or other psychiatric conditions may be associated with complaints of sleepiness, although the MSLT is usually not abnormal. Sleepiness caused by chronically insufficient sleep should improve after a trial of 1 to 2 hours of additional sleep each night. After these diagnoses have been excluded, one is left with the diagnosis of idiopathic hypersomnia.

Management is similar to the approach used for narcolepsy. Patients with the narcoleptic type of sleepiness often respond to stimulants, whereas those with long sleep periods and difficult awakening may not. For most patients, the disorder is chronic. A minority of patients improve with time, and in some, the disorder resolves completely.

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