Comparison of the clinical and electrophysiological characteristics between type 1 and type 2 narcolepsy: a cross-sectional study

Abstract Introduction Narcolepsy is a chronic brain disease characterized by excessive sleepiness and classified into two types based on the presence of cataplexy or reduced level of cerebrospinal fluid orexin-A (hypocretine-1): narcolepsy type 1 (NT1) and narcolepsy type 2 (NT2). These two types differ in symptoms other than cataplexy, as well as in certain examination findings. The present study aimed to investigate the clinical and electrophysiological characteristics of NT1 by comparing its features with those of NT2. Methods Subjects were 118 first diagnosed and untreated patients with narcolepsy. They underwent both polysomnography (PSG) and multiple sleep latency test (MSLT) as a sleep test. Diagnosis was established in accordance with International Classification of Sleep Disorders, Third Edition, and the type of narcolepsy was determined by the presence or absence of cataplexy, patients with cataplexy were diagnosed with NT1, and without cataplexy were diagnosed with NT2. We investigated characteristics of the patients, PSG and MSLT outcomes, and applied a suite of duly statistical analysis to account for each parameter. Results Among the 118 subjects, 35 patients (29.7%) were NT1, and 83 patients (70.3%) were NT2. Excessive daytime sleepiness which was measured by Japanese version of Epworth sleepiness scale (JESS) was significantly higher in NT1 than NT2. Furthermore, the presence of sleep hallucination ( n  = 29, 82.9%), sleep paralysis ( n  = 18, 51.4%), difficult maintaining sleep ( n  = 22, 62.9%), and sleep related movement and behavior disorders ( n  = 7, 20.0%) were significantly higher in NT1 than those in NT2. Additionally, parameters indicative of sleep fragmentation, such as the arousal index and wake time after sleep onset measured in PSG, exhibited a statistically significant increase in NT1 when contrasted with NT2. Conclusions Fragmentation of nocturnal sleep which is explained by the high arousal index and the long wake time after sleep onset on PSG was considered a characteristic finding of NT1 compared with NT2, and the patients with NT1 experienced greater difficulty of maintaining sleep. Concomitantly, the prevalence of NT1 in this study may be a representative value of the prevalence of NT1 among the patients with narcolepsy in Japan.