The Kleine-Levin syndrome. New aspects of a rare disease

The Kleine-Levin syndrome (KLS) is a rare disease which can occur one to several times per year. The KLS belongs to the group of hypersomnia of central origin occurring mainly during the second decade of life after infections, sleep deprivation, alcohol consumption or minor trauma. Early manifestation combined with hypersexuality during symptomatic phases can be a predictor for a long course of the disease, which lasts a mean of 1-27 years. Due to the lack of biological markers diagnosis at first manifestation is difficult. The classical trias of hypersomnia, hyperphagia and hypersexuality can only be found in 45 % of patients. The dominant clinical symptoms are hypersomnia with changes in perception and behavior. Subtraction of perfusion studies performed during symptomatic and asymptomatic phases showed decreased perfusion of the left hypothalamus, thalamus, basal ganglia, medial and dorsolateral frontal and temporal regions. In the few patients who had lumbar punctures in both symptomatic and asymptomatic phases hypocretin-1 was moderately to slightly lowered during symptomatic phases. Meta-analyses showed good therapeutic effects of stimulants on the symptom sleepiness. Lithium reduces the frequency and duration of symptomatic phases. Assuming that KLS is underdiagnosed it should be considered as a differential diagnosis in young patients with recurrent hypersomnia.