This article includes discussion of idiopathic hypersomnia (IH), which is characterized by excessive daytime sleepiness, difficulty awakening (sleep drunkenness), and undisturbed overnight sleep without cataplexy or known cause of excessive sleepiness. Excessive sleepiness (hypersomnolence) of unknown etiology, which cannot be explained by another disorder, would be considered idiopathic hypersomnia. This should be clearly distinguished from other disorders that could present with complaints of excessive daytime sleepiness, such as narcolepsy, behaviorally-induced insufficient sleep, circadian rhythm disturbance, obstructive sleep apnea, or from hypersomnolence secondary to a medical condition or medication. These patients frequently present in adolescence and may have symptoms of autonomic nervous system dysregulation, but they are most often affected because of inability to attend to daytime obligations such as school or work. Because the pathophysiology is unknown, management is limited to symptomatic treatment and education.
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• The main symptom of idiopathic hypersomnia is an irresistible urge to sleep despite adequate, or even excessive, nocturnal sleep, which lasts at least 3 months.
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• For idiopathic hypersomnia duration of sleep (with and without long sleep time) is no longer a criterion for subtype distinction; however, there is a growing body of support for reclassifying idiopathic hypersomnia by sleep duration.
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• Idiopathic hypersomnia can be associated with symptoms of autonomic nervous system dysregulation (orthostatic hypotension, syncope, headache, and Raynaud-type phenomena) and with significant sleep inertia (aka “sleep drunkenness”).
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• The diagnosis of idiopathic hypersomnia is based on clinical features along with testing to rule out other causes of excessive daytime sleepiness (nocturnal polysomnography, multiple sleep latency test, and actigraphy).
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• The differential diagnosis includes other conditions of excessive daytime sleepiness such as narcolepsy, inadequate total sleep time, sleep disorders that impair sleep quality, circadian rhythm disturbances, or hypersomnolence secondary to medical condition or medication.
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• Treatment of idiopathic hypersomnia is primarily symptomatic involving education (sleep hygiene and lifestyle modifications) and off-label usage of wake-promoting agents such as stimulants.
Historical note and terminology
Prior to the use of polysomnographic studies, idiopathic hypersomnia (IH) was usually misdiagnosed as narcolepsy. Dement and colleagues first proposed that a diagnostic category other than narcolepsy should be used for patients who have excessive daytime sleepiness but do not have cataplexy, sleep paralysis, or sleep onset rapid eye movement episodes (33). Subsequently, various labels were proposed to designate this entity: essential narcolepsy (17), non-REM sleep narcolepsy (88), hypersomnia (93), hypersomnia with sleep drunkenness (97), idiopathic hypersomnia (96), idiopathic central nervous system hypersomnia (10), and again idiopathic hypersomnia (07). The previous sleep disorders classification parsed idiopathic hypersomnia into 2 categories based on sleep duration. Idiopathic hypersomnia with long sleep time (> 10 hours) entails excessive sleepiness with prolonged, unrefreshing naps lasting up to 3 or 4 hours, major sleep episodes of at least 10 to 14 hours in duration with difficulty waking up or sleep drunkenness, and no cataplexy. Idiopathic hypersomnia without long sleep time (< 10 hours) reflects excessive sleepiness and unintended, unrefreshing naps, with the major sleep episode lasting less than 10 hours, with difficulty waking up or sleep drunkenness, and no cataplexy (05). The 3rd edition of the International Classification of Sleep Disorders (ICSD-3) no longer dichotomizes idiopathic hypersomnia based on sleep duration (06) (see Table 1). However, built on efforts to better differentiate and refine the primary CNS hypersomnias, a number of experts in the field are calling for a reversal of this framework, given apparent differences between those with long versus short sleep time, particularly with idiopathic hypersomnia with short sleep and NT2 having hardly discernable phenotypes, suggesting excessive sleepiness (hypersomnolence) rather than true excessive sleep duration (hypersomnia) (38; 57).
Table 1. Criteria for Idiopathic Hypersomnia
Idiopathic hypersomnia diagnostic criteria (must meet criteria A to F)
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A. Patient has daily periods of irrepressible need to sleep or daytime lapses into sleep occurring for at least 3 months
B. Cataplexy is absent
C. Multiple sleep latency test (MSLT) shows fewer than 2 sleep onset REM periods or no sleep onset REM periods if the REM latency on the preceding polysomnogram was < or = 15 minutes
D. Presence of at least 1 of the following:
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1. MSLT shows a mean sleep latency of < or = 8 minutes
2. Total 24-hour sleep time is > or = 660 minutes on 24-hour polysomnographic monitoring (performed after correction of chronic sleep deprivation), or by wrist actigraphy in association with a sleep log (averaged over at least 7 days with unrestricted sleep)
E. Insufficient sleep syndrome is ruled out
F. Hypersomnolence and/or MSLT findings are not better explained by another sleep disorder, other medical or psychiatric disorder, or use of drugs or medications
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• Severe and prolonged sleep inertia (sleep drunkenness)
• High sleep efficiency (> or =90%) on polysomnogram
• Total 24-hour sleep time required for diagnosis is adapted based on normal changes in sleep duration for development (children, adolescents) and cultural variance.
Source: International Classification of Sleep Disorders, American Academy of Sleep Medicine, 3rd edition (2014).