Paraneoplastic neuromyelitis optica spectrum disorder manifesting as intractable nausea and acute cerebellar ataxia associated with lung adenocarcinoma

We report a 65‐year‐old woman with neuromyelitis optica spectrum disorder manifesting acute cerebellar ataxia, and intractable nausea and vomiting. She tested positive for anti‐aquaporin 4 antibodies and had a lung adenocarcinoma simultaneously. She underwent partial pulmonary resection, and tumor cells of the lung adenocarcinoma were stained with an anti‐aquaporin 4 antibody. By administering intravenous methyl prednisolone and plasma exchange, aquaporin 4 antibody titer was reduced, and neurological deficits and the lesion status on magnetic resonance imaging markedly improved. Paraneoplastic neuromyelitis optica spectrum disorder in conjunction with lung adenocarcinoma was a reasonable diagnosis.