Swiss Narcolepsy Scale: A Simple Screening Tool for Hypocretin-Deficient Narcolepsy with Cataplexy

Introduction: Narcolepsy is a chronic neurological sleep disorder, the diagnosis of which is based upon clinical evaluation and additional paraclinical assessments. Awareness of narcolepsy is low and screening tools needed. The Epworth Sleepiness Scale (ESS), the Ullanlinna Narcolepsy Scale (UNS), and more recently the Swiss Narcolepsy Scale (SNS) were used as screening tools for narcolepsy. The aims of the present study are (1) to assess the value of the SNS in a new series of patients with narcolepsy with cataplexy (NC), and (2) to compare its sensitivity and specificity with the ESS and UNS. Patients and Methods: We prospectively assessed by questionnaire patients with NC (n = 80, all with assessment of cerebrospinal fluid (CSF) hypocretin-1 levels) and patients with excessive daytime sleepiness (EDS) of other origin (n = 111) in Zurich and Leiden. Causes of EDS included idiopathic hypersomnia (n = 12), behaviorally induced sleep insufficiency syndrome (n = 32), restless legs syndrome (n = 7), sleep-disordered breathing (n = 22), and hypersomnia due to medical disorders (n = 9). Diagnoses were made according to the International Classification of Sleep Disorders (third edition). Cutoff values of UNS and SNS for diagnosis of narcolepsy were those suggested in the literature. Results: For the diagnosis of narcolepsy, the following sensitivities and specificities were found: SNS (89% and 88%), UNS (100% and 62%), and ESS (91% and 54%). For the diagnosis of narcolepsy with low or non-detectable CSF hypocretin-1, the sensitivities and specificities were: SNS (93% and 88%), UNS (100% and 62%), and ESS (93% and 54%). Discussion: In conclusion, the SNS is accurate and superior to the ESS and the UNS for the screening/diagnosis of NC and allows, in addition, the identification of hypocretin-1 deficient patients.