[A case of encephalitis with MRI abnormalities localized in the bilateral amygdala and hippocampus].

We report a patient with encephalitis who showed anterograde and retrograde amnesia with MRI abnormalities localized in the bilateral amygdala (AM) and hippocampus (HIPP). A 25-year-old man suddenly experienced a generalized tonic-clonic seizure (GTCS). He was admitted because of increasing lethargy with two further GTCSs during the following 6 days. The patient had high fever, and neurological examination revealed somnolence, disorientation, amnesia, and nuchal stiffness. MRI revealed bilateral symmetrical abnormalities localized in the AM and HIPP, which showed low intensity on T1-weighted images and high intensity on T2-weighted images. Cerebrospinal fluid examination showed a mildly elevated cell count. We suspected herpes simplex virus type I encephalitis and began treatment with acyclovir. After the patient regained a clear consciousness, his antero- and retrograde amnesia continued for several months. The MRI abnormality became less distinct with the improvement of amnesia. We consider that the MRI abnormality was indicative of inflammation and edema, and that the lesion in the AM and HIPP had induced the amnesia.