Recurrent hypersomnia in an 18-year old boy: CSF hypocretin level and MSLT findings

Abstract

To the Editor: We read with great interest the report by Lopez and colleagues, “Preliminary results on CSF biomarkers for hypothalamic dysfunction in Kleine-Levin syndrome (KLS),” which emphasized recurrent hypothalamic alteration as the pathophysiology of KLS [1]. We commend their serial case reports about cerebrospinal fluid (CSF) biomarker analysis, however, the underlying pathophysiology is still unclear [1,2]. Recently, we had an 18 year-old boy with an incomplete type of KLS. He only complained of recurrent hypersomnia and had no other symptoms of KLS, such as hyperphagia, hypersexuality, behavioral disturbances, and cognitive dysfunction. He had three hypersomnolence attacks lasting for eight to ten days each. We conducted sleep studies and CSF hypocretin measurements in symptomatic and asymptomatic periods. Night polysomnography (PSG) during the symptomatic period revealed a sleep duration of 590 minutes. A Multiple sleep latency test (MSLT) showed a mean sleep latency of 3.4 minutes and five sleep onset REM (SOREM) periods. Threemonths later, his total sleep time during PSGwas only 421minutes and followingMSLT showed normalmean sleep latency, and only one SOREM period. CSF hypocretin revealed 174 pg/ml during the symptomatic episode and 284 pg/ml during the asymptomatic period. The International Classification of Sleep Disorders Third Edition (ICSD-3) decided to use the name ‘Kleine–Levin syndrome’ instead of ‘recurrent hypersomnia’ based on the data suggesting that the condition is almost homogenous [3]. There are no subcategories due to the lack of definite evidence. We believe, however, that this isolated recurrent hypersomnolence is important in the way that each symptom of KLSmight be from different brain lesions, and our results reinforce the hypothesis that hypersomnolence of KLS is due to hypothalamic dysfunction. Thus, hypersomnolence of KLS and narcolepsy might have a similar pathophysiology involving the posterior hypothalamus, temporary dysfunction in KLS and complete destruction in narcolepsy.