A Case of Paraneoplastic Limbic Encephalitis in a Patient with Invasive Thymoma with Anti-Glutamate Receptor Antibody-Positive Cerebrospinal Fluid: A Case Report

Background: Thymoma is known to cause autoimmune neuromuscular disease. However, anti-glutamate receptor antibody limbic encephalitis (LE) with thymoma is relatively rare. Case Presentation: A 68-year-old woman was admitted with progressive memory impairment and personality change. Brain magnetic resonance imaging (MRI) revealed high intensity in the bilateral limbic areas on T2-weighted fluid-attenuation inversion recovery (FLAIR) images. Chest computed tomography revealed a mass in the anterior mediastinum. Surgical resection of the tumor, which was consistent with a type B3 thymoma, resulted in clinical improvement. After surgery, the cerebrospinal fluid (CSF) was found to be positive for anti-N-methyl-D-aspartate (NMDA) type glutamate receptor antibodies. These findings led to the diagnosis of paraneoplastic LE (PLE) associated with thymoma. Conclusion: When a patient presents with neurologic symptoms of unknown origin, the possibility of LE accompanied by thymoma should be considered. Rapid treatment is desirable before the symptoms become irreversible.