46 Chapter 2 Here we use a data-driven approach to compare the numbers of NT1 patients presenting symptoms before, during and a few years post the 2009–2010 pH1N1 in EU-NN database. We aim to (1) test whether the increased NT1 peak was indeed unique for the 2009–2010 pH1N1 [136] or repeated over time, compatible with the multiple-hit hypothesis. Recurrent increased incidences indicate that immune-mediated narcolepsy is not necessarily specific to H1N1/Pandemrix; (2) identify possible differences between different age groups related to the increased NT1 incidence. Adults may be less influenced by influenza virus to develop NT1 because those potential candidates developing NT1 probably already have had enough hits to trigger NT1. Methods Each centre of EU-NN has obtained ethical approval for publishing the patients’ data for scientific purpose by a national Institutional Review Board before entering patients. The scientific review committee of EU-NN has approved the study protocol. All methods are in accordance with the relevant guidelines and regulations. All patients have provided their informed consent to be entered into the EU-NN database and their data can be used for scientific studies. Patients with NT1 were diagnosed according to the third edition of International Classification of Sleep Disorders (ICSD-3) [8]. Patients with daily periods of the irrepressible need to sleep or daytime lapses into sleep occurring for at least 3 months and the presence of at least one of the following: 1. Cataplexy and mean sleep latency of 8 min or less and at least two sleep onset rapid eye movement periods (SOREMPs) on a multiple sleep latency test (MSLT). A SOREMP on the preceding nocturnal polysomnography may replace one of the SOREMPs on the MSLT. 2. Cerebrospinal fluid (CSF) hypocretin-1 concentration, measured by immunoreactivity, is after conversion to Stanford values either 110 pg/ mL or less, or less than one third of mean values obtained in normal subjects using the same standardized assay. The following criteria were used to exclude NT1 patients from the EU-NN database for our analysis: 1. Patients with an indefinite diagnosis. The EU-NN database contains a variable on certainty of clinical diagnosis. The clinicians were asked to rate their diagnostic certainty on a 3-level scale (probable, possible,
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