66 Chapter 3 season severity and NT1 incidence holds true for Europe and whether other influenza strains could also be linked to NT1 onset, remains to be investigated. Most interestingly, among the dominant influenza strains in the 2012-2013 influenza season (preceding the 2013 NT1 peak in children) was type B influenza in many European countries [149]. This suggests that type B influenza could also be a potential trigger for narcolepsy [159]. Previous analyses only focused on onset of NT1 and lacked inclusion of other central disorders of hypersomnolence (CDH). Narcolepsy type 2 (NT2) and idiopathic hypersomnia (IH) share the complaint of EDS but in the absence of cataplexy and without hypocretin deficit in the cerebrospinal fluid (CSF). The pathophysiologies of these disorders remain elusive but recent findings have suggested frequent reports of respiratory infections close to onset of NT2 and IH [163]. A possible relationship with influenza infections has not yet been carefully studied. The main aim of the current study was to first investigate NT1, NT2 and IH incidence rates between 2010-2019 (following the pH1N1) using complete samples from multiple European sleep-wake clinics. We additionally correlated incidence rates to detailed yearly influenza season severity data within each country, while taking into account distributions of different influenza strains. Type A influenza was included for all countries, and type B influenza data was only available for the Netherlands. We hypothesized a significant correlation between type A H1N1 and possibly type B influenza and NT1 incidence rates in children. Methods All people with CDH who attended one of our specialized sleep-wake clinics between January 2010 and December 2019 were included in this observational study. Clinics included Sleep-Wake Centre SEIN in Heemstede (the Netherlands, total sample is N=295), Montpellier (France, N=619), Bologna (Italy, N=246), Prague (Czech Republic, N=156), Warsaw (Poland, N=94), Kosice (Slovak Republic, N=37), Innsbruck (Austria, N=45) and Madrid (Spain, N=34). Medical records were retrospectively reviewed and detailed data were extracted on the symptoms (EDS and cataplexy presence, and EDS date of onset and Epworth Sleepiness Scale score, ESS), sleep test results (multiple sleep latency test [MSLT] mean sleep latency and sleep-onset rapid eye movement period [SOREMP] count and polysomnography SOREMP presence) and objective biomarkers (CSF hypocretin-1 levels, and HLA-DQB1*06:02 positivity). Hypersomnolence diagnoses were compliant with ICSD-3 criteria and individuals were classified as having NT1 or NT2, or IH [8]. Centres generally performed a diagnostic
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