Elsevier

Neurologic Clinics

Volume 14, Issue 3, 1 August 1996, Pages 573-582
Neurologic Clinics

IDIOPATHIC HYPERSOMNIA

https://doi.org/10.1016/S0733-8619(05)70274-7Get rights and content

In comparison with narcolepsy, which is characterized by well-defined clinical, polysomnographic, and immunogenetic features, idiopathic hypersomnia is not well delineated and its history is much more recent.

In 1966, Dement et al10 proposed that subjects with excessive daytime sleepiness but no cataplexy, sleep paralysis, or sleep-onset rapid eye movement (REM) periods should not be considered narcoleptic. Subsequently, Berti-Ceroni et al6 and Passouant et al22 described narcolepsy with non–rapid eye movement (NREM) sleep episodes. The clinical picture was still vague, however, and it is very likely that among the subjects under consideration were subjects with other sleep disorders, including respiratory disorders associated with sleep. In 1972, Roth et al28 circumscribed the limits of the condition in describing a type of “hypersomnia with sleep drunkenness,” which consisted of difficulty in coming to complete wakefulness accompanied by confusion, disorientation, poor motor coordination, and slowness associated with deep and prolonged sleep. Four years later, the same group proposed a classification of hypersomnolent conditions, which included narcolepsy, hypersomnia, and the subwakefulness syndrome.25 Hypersomnia was considered either symptomatic or functional, with the functional form subdivided into a functional hypersomnia with a short cycle and a functional hypersomnia with a long cycle (periodic hypersomnia). Functional hypersomnia with a short cycle was further subdivided into idiopathic hypersomnia and neurotic hypersomnia. Finally, idiopathic hypersomnia was considered either monosymptomatic, manifested only by excessive daytime sleepiness and not by abnormal awakening, or polysymptomatic, characterized by excessive daytime sleepiness, nocturnal sleep of abnormally long duration, and signs of “sleep drunkenness” on awakening.

According to the International Classification of Sleep Disorders (ICSD),3 idiopathic hypersomnia is “a disorder of presumed central nervous system cause that is associated with a normal or prolonged major episode and excessive sleepiness consisting of prolonged (1–2 hours) sleep episodes of NREM sleep.” Clearly, the ICSD definition merges Roth's monosymptomatic and polysymptomatic forms by indicating that some patients report great difficulty waking up and experience disorientation after awakening.

Finally, based on a retrospective review of clinical and polygraphic findings and questionnaire results in groups of subjects with narcolepsy, narcolepsy without cataplexy, idiopathic hypersomnia, insufficient sleep syndrome, mild sleep apnea, and excessive daytime sleepiness not otherwise specified, Aldrich2 suggests that the syndrome of idiopathic hypersomnia is a heterogeneous syndrome. He also reports that relatively few patients have the polysymptomatic form of idiopathic hypersomnia described by Roth25 and that other subjects experience prolonged sleep without sleep drunkenness, excessive daytime sleepiness without prolonged sleep hours, a clinical syndrome with sleep paralysis, or sleep-related hallucinations clinically indistinguishable from narcolepsy without cataplexy but without REM sleep abnormalities.

Section snippets

PREVALENCE

Because of the somewhat vague limits of idiopathic hypersomnia and its relative rarity, no prevalence study has ever been conducted. The only available data are the ratios of idiopathic hypersomnia to narcolepsy in different sleep disorders populations (Table 1). The ratios tend to decrease in the successive reports, probably due to the use of more stringent criteria, with the notable exception, however, of Aldrich's2 recent series.

AGE OF ONSET

In contrast with narcolepsy, a precise onset of idiopathic hypersomnia is often difficult to determine because of the insidious beginning of the condition and the difficulty, in young persons, of settling a posteriori a limit between long sleep and abnormally long sleep or normal wakefulness and impaired wakefulness. As is the case for narcolepsy and the Kleine-Levin syndrome, however, onset of this condition is most often during adolescence and rarely after the age of 30 years (Fig. 1).

CLINICAL FEATURES

The symptoms of idiopathic hypersomnia may vary.2 The most typical form, which Roth et al25 referred to as polysymptomatic, is characterized by excessive daytime sleepiness leading to unrefreshing prolonged naps, nocturnal sleep of long duration (as much as 12 hours or more), and sleep drunkenness. Subjects affected with this type of idiopathic hypersomnia often refrain from naps because of their spontaneous long duration and their unrefreshing nature. They use sophisticated alarm clocks and

COURSE

Idiopathic hypersomnia is a life-long disorder with no tendency to remit spontaneously. Complications are mostly social and professional.1, 8 Whether subjects' symptoms can be temporarily alleviated by having their sleep extended has not been investigated.

DIAGNOSTIC PROCEDURES

The diagnosis of idiopathic hypersomnia is mainly based on clinical features and the absence of associated symptoms such as cataplexy, snoring at night, periodic leg movements, or depression. Polysomnography and some other tests are necessary to rule out other sleep disorders, however. Indeed, in the author's experience, idiopathic hypersomnia is one of the most overdiagnosed sleep disorders.

The most widely used polysomnographic procedure is nocturnal sleep recording followed by a multiple

PATHOPHYSIOLOGY

In contrast with narcolepsy, no animal model of idiopathic hypersomnia is available; thus, experimental approaches are limited. Destruction of noradrenergic neurons of the rostral third of the locus coeruleus complex or of the noradrenergic bundle at the level of the isthmus in the cat, however, leads to hypersomnia with a proportional increase of NREM sleep and REM sleep, resembling idiopathic hypersomnia. This state is accompanied by a decrease of diencephalic norepinephrine.23

Not much

TREATMENT

Treatment of idiopathic hypersomnia is far from satisfactory. Stimulant drugs, such as dextroamphetamine, methylphenidate, mazindol, or pemoline, are the most commonly prescribed medications. These drugs often are less effective in idiopathic hypersomnia than in narcolepsy, however, and sometimes not as well tolerated. Recently, a new compound, modafinil, the mechanism of which is still unclear, produced good results in subjects with idiopathic hypersomnia.5 A double-blind controlled study has

SUMMARY

Idiopathic hypersomnia is not as well delineated as narcolepsy and its history is much more recent. There are at least two forms of the disorder: (1) a polysymptomatic form, characterized by excessive daytime sleepiness, nocturnal sleep of abnormally long duration, and signs of sleep drunkenness on awakening, and (2) a monosymptomatic form that manifests only by excessive daytime sleepiness. The most widely used laboratory procedures are nocturnal polysomnographic recording followed by an MSLT

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    Address reprint requests to Michel Billiard, MD, Neurology B Department, Gui-de-Chauliac Hospital, 34295 Montpellier, Cedex 05, France

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    From the Neurology B Department, Gui-de-Chauliac Hospital, Montpellier, France

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