MSD Manual

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Idiopathic Hypersomnia


Richard J. Schwab

, MD,

  • University of Pennsylvania, Division of Sleep Medicine

Last full review/revision Jun 2020| Content last modified Jun 2020
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Idiopathic hypersomnia is excessive daytime sleepiness with or without a long sleep time; it is differentiated from narcolepsy by lack of cataplexy, hypnagogic hallucinations, and sleep paralysis.

Idiopathic hypersomnia is not well-characterized. Cause is presumed to be dysfunction of the central nervous system.

Excessive daytime sleepiness is the main symptom; sleep time may or may not be prolonged.


  • History or sleep logs

  • Sleep tests

In idiopathic hypersomnia with a long sleep time, the history or sleep logs indicate > 10 hours of nocturnal sleep; in idiopathic hypersomnia without a long sleep time, it is > 6 hours but< 10 hours. In both cases, polysomnography shows no evidence of other sleep abnormalities. Multiple sleep latency testing shows short sleep latencies (< 8 minutes) with fewer than 2 REM periods.


  • Similar to that of narcolepsy

Treatment of idiopathic hyperinsomnia is similar to that of narcolepsy (eg, modafinil), except that anticataplectic drugs are unnecessary.

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