Herpes simplex encephalitis presenting with bilateral hippocampal lesions on magnetic resonance imaging, simultaneously complicated by small cell lung carcinoma.

We report a 75-year-old man who developed herpes simplex encephalitis (HSE), presenting with bilateral hippocampal lesions on magnetic resonance imaging, and this case was simultaneously complicated by small cell lung carcinoma. We identified a new anti-neuronal antibody in the cerebrospinal fluid of this patient. Our findings suggest that HSE and paraneoplastic limbic encephalitis (PLE) can overlap, and we discuss the relationships of HSE, PLE, and related disorders.