GABA_BR-Mediated Paraneoplastic Limbic Encephalitis Due To Thymic Small Cell Carcinoma

We report the case of a 55-year-old male who presented with several weeks of seizures, agitation, progressive confusion, and receptive aphasia. CSF showed a monocytic pleocytosis and tested positive for GABA_B receptor autoantibodies. Pathological examination of an excisional mediastinal lymph node biopsy showed thymic small cell carcinoma, supporting a diagnosis of paraneoplastic limbic encephalitis (PLE). PLE is a subtype of limbic encephalitis and is associated with an array of autoantibodies. Neurologic symptoms related to PLE may precede the detection of the primary cancer. Recognition of the constellation of clinical features of limbic encephalitis should prompt initiation of diagnostic testing for this condition as well as evaluation for an underlying malignancy. A review of the literature reveals that this is the first case report of a patient with thymic small cell cancer presenting with PLE.