Clinical characteristics of symptomatic narcolepsy or hypersomnia: an analysis of 182 consecutive cases with neurological disorders associated with hypersomnolence

Purpose Symptomatic narcolepsy is characterized as low orexin (hypocretin) levels (≤ 110 pg/ml) due to neurological diseases. However, we have experienced the cases that show symptoms similar to narcolepsy, complaining of pathological sleepiness even in cases with intermediate orexin levels (110–200 pg/ml). Therefore, we reevaluated the previously reported cases to make the concept of disease to the group in which the orexin concentration is intermediate. Methods Although orexin-deficient symptomatic narcolepsy has been reported worldwide, facilities that are capable of measuring orexin are still limited. Currently, our laboratory handles with almost all the CSF samples from Asian countries for determining orexin levels. We measured over 2500 cases including 182 cases suspected of symptomatic narcolepsy/hypersomnolence. Therefore, we subdivided these cases into three groups according to CSF orexin levels, low orexin group (≤ 110 pg/ml), intermediate orexin group (110–200 pg/ml), and normal orexin group (> 200 pg/ml). We defined “symptomatic hypersomnia” for hypersomnolence cases with intermediate CSF orexin levels. MSLT was recommended but not necessary. Short sleep latency (