Kleine-Levin Syndrome.

Kleine-Levin syndrome (KLS) is a rare disorder characterized by discrete episodes of hypersomnia associated with cognitive and behavioural abnormalities, as well as normal alertness and function between episodes. The prevalence of KLS may be underestimated as it is often misdiagnosed and managed as another sleep disorder, neurological disorder or psychiatric condition. KLS is more typically seen in adolescence than at other ages, and is more common in males than in females. There are currently neither standard biomarkers nor specific imaging study findings, making the diagnosis of KLS a challenge. Furthermore, there are no consistently effective therapies. The prognosis, however, is felt to be overall favorable, as episodes become progressively milder and less frequent before resolving entirely in most patients.