Kleine-Levin syndrome. Clinical boarderlands based on a thorough analysis of 475 case reports

Kleine-Levin syndrome (KLS) is a rare sleep disorder characterized by recurrent episodes of severe hypersomnolence in association with various degrees of cognitive impairment, perceptive abnormalities, apathy, behavioral disturbances. Some of these symptoms, hypersomnolence, compulsive eating and increased sexual drive may be replaced by their opposites or alternate with them. Remarkably enough, these « atypical symptoms » have never been enlighted nor compared in frequency with corresponding typical symptoms. Besides, KLS is more frequent in males than in females but no review has ever compared the frequency of precipitating factors and symptoms in males and females. To uncover these as yet uninvestigated aspects of KLS, a predesigned template was used to extract precipitating factors and symptoms, in 475 case reports of KLS, comprising 364 males and 111 females. Precipitating factors were more frequently recorded in males (67.31 %) than in females (49.55 %). Recurrent episodes of hypersomnolencee were present in 94.32 % of cases, recurrent insomnia in 1.05 % and alternation of hypersomnolence and insomnia in 4.63 %. Cognitive impairment was present in 67.37 % of cases and absent in 6.95 %. Derealization/altered perception was present in 38.32 % of cases and absent in 1.68 %. Severe apathy was present in 44.63 % of cases. Compulsive eating was present in 59.58 % of cases, absent in 13.26 %, replaced by anorexia in 9.05 %, alternation of compulsive eating and anorexia in 5.68 % and alternation of compulsive eating and no compulsive eating in 8.42 %. Increased sexual drive was present in 33.68 % of cases, absent in 22.74 %, replaced by decreased sexual drive in 1.47 %, alternation of increased sexual drive and no increased sexual drive in 2.95 %. Odd behaviors were present in 45.05 % of cases. Psychiatric features were present in 71.58 % of cases, absent in 2.95 %. Finally, the percentages of precipitating factors and of sleep disorder, apathy, sexual disorder, irritability/agressivity, were higher in males than in females. The frequency of the opposites of hypersomnolence, compulsive eating and increased sexual drive appears to be quite significant. In addition, a systematic comparison of precipitating factors and symptoms in males and females has shown limited differences between sexes. •Naming of Kleine-Levin symptoms must be standardized.•A review of KLS symptoms must include presence, absence and absence of data.•Hypersomnolence, hyperphagia, hypersexu