• Ji Yeon Chung, Chang Ju Lee, Jeong Bin Bong, Byoung-Soo Shin, Han Uk Ryu, and Hyun Goo Kang.
• Department of Neurology, Chosun University Medical School, Gwangju, South Korea.
• Medicine (Baltimore). 2023 Oct 27; 102 (43): e35566e35566.

RationaleNeuromyelitis optica spectrum disorder (NMOSD) is a demyelinating disease that causes lesions in areas with abundant aquaporin-4 (AQP4) channels, including the hypothalamus. Hypothalamic lesions can disrupt antidiuretic hormone regulation, resulting in hyponatremia due to syndrome of inappropriate antidiuretic hormone (SIADH). Various factors can trigger NMOSD, including viral infections. We report the case of a young female patient who presented with hyponatremia due to SIADH and was found to have bilateral hypothalamic lesions along with positive serum herpes simplex virus immunoglobulin M.Patient ConcernsAn 18-year old female patient presented with fever and nausea that had persisted for 5 days. Three days after hospitalization, the patient complained of blurred vision, hiccups, and excessive daytime sleepiness.DiagnosisThe patient hyponatremia was attributed to SIADH. Magnetic resonance imaging revealed bilateral lesions in the hypothalamus, and serum laboratory tests were positive for herpes simplex virus immunoglobulin M. On the 15th day of admission, the anti-AQP4 antibody test result was positive, leading to the diagnosis of NMOSD.InterventionsOn the initial suspicion of herpes encephalitis, treatment with acyclovir was initiated. However, upon the confirmation of after anti-AQP4 antibody, the patient was additionally treated with a high-dose intravenous steroid for 5 days.OutcomesThe patient fever, nausea, visual disturbances, and other complaints improved within 1 week of initiating steroid treatment.LessonsIn young patients presenting with hyponatremia and suspected SIADH accompanied by neurological abnormalities, it is crucial to differentiate central nervous system diseases, including NMOSD, which can involve lesions in AQP4-abundant areas, such as the hypothalamus.Copyright © 2023 the Author(s). Published by Wolters Kluwer Health, Inc.

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