Symptomatic narcolepsy type 2 in a patient with AQP4–positive neuromyelitis optica spectrum disorder

A 63-year-old woman, previously diagnosed with multiple sclerosis (MS) and treated with IFNβ-1b, developed asymptomatic lesion expansion surrounding the thalamus and basal ganglia. However, an AQP4 autoantibody ELISA was negative. The patient was subsequently hospitalized due to drowsiness, lethargy, and difficulty in managing housework. During lumbar puncture, the patient lost consciousness. Electroencephalography (EEG) revealed rapid eye movements, and a multiple sleep latency test (MSLT) indicated narcolepsy. Cerebrospinal fluid (CSF) orexin levels were normal, and no cataplexy was observed. The patient was thus diagnosed with narcolepsy type 2. The patient tested positive for AQP4 antibody, and was diagnosed with neuromyelitis optica spectrum disorder (NMOSD). Sleep physiology testing is crucial because some patients with NMOSD do not exhibit hypothalamic lesions or decreased CSF orexin levels.