LAUSR

To the Editor: Recent discovery of the immunologicalmechanismdamaging the hypocretin neurons in the lateral hypothalamus in narcolepsy type 1 (NT1) indicates that early intervention close to case onset might stop this immunological process or even reverse the destruction of hypocretin neurons [1, 2]. In previous case reports, plasmapheresis, corticosteroids, intravenous immunoglobulin infusions, alemtuzumab, and rituximab were used with mixed outcomes [3, 4]. Here, we report a child with recent-onset NT1and a suspicion of neuromyelitis optica spectrum disorder (NMOSD) treated with different immune modulators. The clinical course of the patient is shown in Fig. 1. In November 2016, about 7 months before presentation, a 5 yearold boy had upper airway infection with fever. He started to experience excessive daytime sleepiness (EDS) and cataplexy in late June 2017. He could fall asleep at anytime such as when playing, eating, and watching TV. Cataplexy involving the knees, mouth, and neck could be elicited by emotional changes, such as laughter.The cataplexy was so severe that the boy could not walk by himself. He had severe nocturnal sleep disturbance but no sleep paralysis or hypnagogic hallucinations. Nocturnal polysomnography (nPSG) followed by a daytime multiple sleep latency test (MSLT) was under taken 10 days after the onset of EDS. nPSG showed a nocturnal sleep latency (SL) of 7 min, rapid eyemovement (REM) latency of 145.5min, no sleep apnea or periodic limbmovement disorder.MSLT indicated amean SL of 6.4 min and four sleep onset REM periods (SOREMPs) in 5 naps. Then, methylphenidate at a dose of 18 mg was given. Although daytime sleepiness improved slightly, cataplexy did not. Neurological examination, electroencephalogram, and routine cerebrospinal fluid (CSF) examination showed no remarkable findings. No optic involvement was detected by ophthalmologic examination, except for slightly increased visual evoked potential (EVP) P1 latency of both left and right side(L = 125 ms, R = 182.5 ms, respectively, normal range < 108 ms). Screening for neuronal autoantibodies, including anti-NMDA receptor antibody, anti-GABA-breceptor antibody, anti-LG1 antibody, antiCASPR2 antibody, antiglycine receptor antibody, anti-Hu/Ri/Yo antibody, antiCV2 antibody, anti-PNMA2 antibody, antiamphiphysin antibody, anti-MBP antibody, and anti-MOG antibody,was all negative in both serum and CSF. Antiaquaporin 4 antibody (AQP4) tested with tissue-based assays was negative in serum and CSF. Oligoclonal bands in CSF were negative. IgG index in CSF slightly elevated (0.89, normal range <0.85). Abnormal high signals in the right cerebellum and brachium pontis were revealed in FLAIR of brain magnetic resonance imaging (MRI), and neuromyelitis optica spectrum disorder (NMOSD) was initially suspected in the local hospital. Intravenous immunoglobulin (IVIg) at a dose of 2 g/kg/day for 4 days was given5 weeks after the MSLT. No symptom improvement was noticed. The patient was then given a high dose of methylprednisolone 0.5 g/day for 3 days per week for three consecutive weeks. EDS and nocturnal sleep disturbance improved remarkably after the first 3 day dose ofmethylprednisolone. Cataplexy decreased from > 10 times per day to < 5times per day. Neurophysiologically, EVP P1 latency of both sides deceased,with the right side returning to normal (from 182.5 to 103.8 ms, normal <108 ms). Oral prednisolone at a dose of 55 mg/day was given and tapered gradually. Three months after intravenous prednisolone, on daily oral prednisolone of 35 mg, the frequency of cataplexy returned to > 10 times/day. A second screening for neuronal autoantibodies showed that serum NMO-IgG/anti-AQP4 antibody was Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11325-020-02034-z) contains supplementary material, which is available to authorized users.