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 CNS dysfunction.

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

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

Treatment is similar to that of narcolepsy, except that anticataplectic drugs are unnecessary (see Sleep and Wakefulness Disorders: Treatment).

Last full review/revision November 2012 by Karl Doghramji, MD