ABSTRACT
INTRODUCTION The Kleine-Levin syndrome (KLS) was initially named by Critchley, who reviewed previous case reports by Willi Kleine (1) and Max Levin (2,3), and described 11 additional cases in young adults (4,5). The hallmark of the syndrome is periodic extreme hypersomnia. At that time, excessive daytime somnolence had been mainly attributed to either narcolepsy or the Pickwickian syndrome/obstructive sleep apnea (6). These were known as chronic somnolence states, while the major novel description by Kleine, Levine, and Critchley was the periodic nature of this new syndrome, as well as the association to attacks of hyperphagia. Since these initial reports, there were quite a number of case reports published, some on a fairly large group of patients, but population-based studies have not been performed. The largest summary work so far on this topic was carried out by Arnulf et al. (7), who systematically reviewed previous publications on KLS, added them into one database, and analyzed 186 recognized cases. Two relatively large studies on KLS (descriptions of 34 and 30 patients) were not included, due to potential overlap with other publications and lack of sufficient individual data (8,9). In all cases attacks were associated with hypersomnolence (100%) (7). Additional characteristics of attacks consisted of cognitive changes (96%), eating disturbances (80%), depressed mood (48%), hypersexuality (43%), and compulsions (29%). It is generally accepted that this is a rare disease, but probably under-diagnosed. However, the frequency may be somewhat higher in specific communities/ethnics. The incidence of reported cases in Israel is relatively high, as it may be more prevalent among Jews (9,10). A significantly increased Jewish predisposition of KLS was observed in the U.S. as well, where 15% of KLS patients were Jews versus 2% Jewish in the general population (7). While KLS affects approximately one in a million people in the U.S., the 34 patients reported in Israel in 2001 (approximately six million population) yield a prevalence that is approximately sixfold (9).
