[Non-herpetic acute limbic encephalitis].

We reported four cases of acute encephalitis, in which MRI abnormalities localized in the limbic system. In the four cases, fever and consciousness disturbance were commonly found and convulsive seizures appeared in three. Within 10 days, their consciousness level became clear, but severe amnestic syndrome remained as sequela. Cerebrospinal fluid (CSF) at the acute stage revealed mild lymphocytic pleocytosis and elevated protein. MRI revealed abnormal signal intensities in both hippocampi and amygdaloid bodies, although CT scans were normal. Herpes simplex encephalitis selectively affects one or both temporal lobes and the limbic system, But our cases spared the temporal lobes. Additionally, serum and CSF antibody titers by CF and ELISA for herpes simplex virus (HSV) were within normal range from the acute to convalescent stages. Neither HSV type 1 and 2 DNA genomes by sensitive PCR-hybridization method were detected in CSF taken from the acute stage of all four cases. On the other hand, paraneoplastic limbic encephalitis is known as a subacute encephalitis predominantly involving the limbic system. MRI shows high signal intensities on T2-weighted in both medial temporal lobes. In our cases, this type of limbic encephalitis was excluded because of the acute onset and lack of malignancy. Accordingly, our four cases are regarded as non-herpetic acute limbic encephalitis. Several Japanese similar cases have been reported. Further etiological studies should be performed.