[A Case of Paraneoplastic Neurological Syndrome Caused by Bladder Cancer Manifesting as Limbic Encephalitis].

A woman in her 40s underwent transurethral resection of bladder tumor in September X-2 followed by preoperative chemotherapy for muscle-invasive bladder cancer. She later had robot-assisted radical cystectomy with neobladder cystostomy in February X-1. In July X-1, computed tomography revealed metastasis in the right pulmonary apex and right upper mediastinal lymph node, and a partial resection of these sites was performed. Based on the pathological results, the patient was diagnosed with bladder cancer metastasis. Pembrolizumab was started in December X-1 ; however, right upper mediastinal lymph node enlargement was noted in October X, with progressive growth. In December X, the patient visited her primary care physician due to amnesia and decreased attention. Magnetic resonance imaging (MRI) revealed abnormal signal areas in the right temporal pole and the medial portions of both temporal lobes. Her symptoms worsened after a week, prompting steroid pulse therapy for suspected limbic encephalitis. Although her brain MRI revealed some improvement, her symptoms persisted. Repeated steroid pulse therapy had no effect. Following intravenous immunoglobulin, the patient's symptoms and MRI findings improved. Based on these findings, she was diagnosed with limbic encephalitis due to bladder cancerassociated paraneoplastic neurological syndrome.