Abstract
Kleine–Levin syndrome is a rare disorder characterized by relapsing-remitting episodes of severe hypersomnia, cognitive impairment, apathy, derealization and behavioural disturbances. Between episodes, most patients experience normal sleep, mood and behaviour, but they may have some residual abnormalities in brain functional imaging; however, the frequency, localization and significance of abnormal imaging are unknown, as brain functional imaging have been scarce and heterogenous [including scintigraphy 18F-fluorodeoxyglucose positron emission tomography/computerized tomography (FDG-PET/CT) and functional MRI during resting state and cognitive effort] and based on case reports or on group analysis in small groups. Using visual individual analysis of 18F-fluorodeoxyglucose positron emission tomography/computerized tomography at the time of Kleine–Levin syndrome diagnosis, we examined the frequency, localization and clinical determinants of hypo- and hypermetabolism in a cross-sectional study. Among 179 patients with Kleine–Levin syndrome who underwent 18F-fluorodeoxyglucose positron emission tomography/computerized tomography, the visual analysis was restricted to the 138 untreated patients studied during asymptomatic periods. As many as 70% of patients had hypometabolism, mostly affecting the posterior associative cortex and the hippocampus. Hypometabolism was associated with younger age, recent (<3 years) disease course and a higher number of episodes during the preceding year. The hypometabolism was more extensive (from the left temporo-occipital junction to the entire homolateral and then the bilateral posterior associative cortex) at the beginning of the disorder. In contrast, there was hypermetabolism in the prefrontal dorsolateral cortex in half of the patients (almost all having concomitant hypometabolism in the posterior areas), which was also associated with younger age and shorter disease course. The cognitive performances (including episodic memory) were similar in patients with versus without hippocampus hypometabolism. In conclusion, hypometabolism is frequently observed upon individual visual analysis of 18F-fluorodeoxyglucose positron emission tomography/computerized tomography during asymptomatic Kleine–Levin syndrome periods; it is mostly affecting the posterior associative cortex and the hippocampus and is mostly in young patients with recent-onset disease. Hypometabolism provides a trait marker during the first years of Kleine–Levin syndrome, which could help clinicians during the diagnosis process.
Highlights
Kleine–Levin syndrome (KLS) is a rare (3/million) neurological disorder affecting mostly teenagers or young adults
Patients with atypical or differential diagnoses, those with KLS secondary to other disorders and those with severe mental deficiency were excluded. This cohort of KLS patients was different from the 41 patients with KLS who benefitted from single photon emission computed tomography (SPECT) analysis between 2007 and 2011.13 For this analysis, patients who had the FDG-PET/CT during an episode were excluded, as well as those already treated for KLS at the time of the scan
Because the hippocampus is involved in memory processes, we evaluated whether cognitive impairments correlated with hypometabolism in this structure in an exploratory study (Table 4)
Summary
Kleine–Levin syndrome (KLS) is a rare (3/million) neurological disorder affecting mostly teenagers or young adults. The syndrome is characterized by recurrent, relapsing-remitting episodes of severe hypersomnia, cognitive impairment, apathy and derealization, sometimes associated with disinhibited behaviour (megaphagia, hypersexuality and rudeness), altered mood and hallucinations.[1] Sleep, mood, cognition and behaviour are usually normal between episodes, some mild cognitive abnormalities may persist during asymptomatic periods,[2,3] as well as emerging psychiatric disorders in 20% of patients.[4] The mechanisms and causes of KLS are unknown, but autoimmune or inflammatory hypotheses are suggested. The diagnosis is clinical, as there is yet no identified marker in the cerebrospinal fluid, and morphological brain imaging is normal.[5] the diagnosis is easy in the presence of clear-cut brief (e.g. 1 week) episodes with severe symptoms in adolescents, but it is more difficult in cases with unsure or absent history, amnesia, long episodes, attenuated or unusual symptoms and concomitant psychiatric or neurological disorders
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