Significance of determining plasma orexin levels and analysis of related factors for the diagnosis of patients with narcolepsy.

Objectives: Decreased cerebrospinal fluid (CSF) orexin levels are one of the diagnostic and classification criteria for narcolepsy. Because of the difficulty in obtaining CSF, its clinical application is limited. Here, we aimed to confirm the significance of determining plasma orexin levels in the diagnosis and treatment of narcolepsy by comparing the differences in these levels between narcolepsy patients and healthy controls and analyzing related factors.

Methods: Twenty-four patients with type I narcolepsy who visited our hospital from October 2017 to January 2020 and who met the relevant inclusion and exclusion criteria were selected. Simultaneously, healthy controls with matched basic characteristics were selected at a 1:1 proportion. Patient basic information was collected, the Epworth Sleepiness Scale was recorded, the nocturnal polysomnogram and multiple sleep latency test were performed, and the patients' electrophysiological characteristics were analyzed. The blood samples of the patient and control groups were collected and stored at -80°Caftercentrifugation. Plasma orexin levels were determined by ELISA, following which the results of the two groups were compared, and the relevant factors were analyzed.

Results: Our results revealed significantly lower plasma orexin levels in the narcolepsy patients compared to in healthy subjects. There were no correlations between plasma orexin levels and sex, age, body mass index, disease duration, and the severity of sleepiness, and between plasma orexin levels and electrophysiological indicators, including mean sleep latency and sleep-onset rapid eye movement periods.

Conclusions: Determining plasma orexin levels has the potential to replace the detection of CSF orexin levels.