Section Editor: Sandy Cheng-Yu Chen, M.D.
Taipei Medical University Hospital, Taipei, Taiwan
Paraneoplastic limbic encephalitis is a result of the production of antibodies against antigens by the malignant cells of some types of cancer that cross-react with normally expressed neuronal antigens. The most commonly associated neoplasm is small cell lung cancer. Patients typically present with seizures and prominent behavioral symptoms or memory deficits. MR imaging findings that suggest limbic encephalitis are T2-hyperintense signals in one or both medial temporal lobes (A, arrows), usually without enhancement after contrast (B, arrows). Our case is paradigmatic for the absence of a previous cancer diagnosis. The detection of anti-GABAB receptor antibodies in serum and CSF prompted the search for an underlying malignancy; PET-CT revealed a hypermetabolic right pulmonary hilar lesion (C, arrow) and a follow-up transbronchial needle aspiration confirmed secondary adenopathic involvement of small cell lung cancer.