MRIで両側の扁桃核と海馬に限局した異常が描出された脳炎の1例

A Case of Encephalitis with MRI Abnormalities Localized in the Bilateral Amygdala and Hippocampus

　両側の扁桃核と海馬に限局した異常を呈し，著明な前向性健忘と過去2年間の逆向性健忘がみられた脳炎の1例を報告した。症例は25歳の男性で，突然の全身性強直性間代性痙攣で発症した。その後，記銘力の低下，先見当識，さらに2回の全身性強直性間代性痙攣が出現し，入院した。入院時，発熱がみられ，神経学的には，失見当識，傾眠傾向，健忘，項部硬直がみられた。MRIでは，両側の扁桃核と海馬に限局したT1強調像で低信号を，T2強調像で高信号を呈する異常が描出された。髄液検査では，軽度の細胞数の増多がみられた。単純ヘルペスI型脳炎を疑いアシクロビルを投与した。意識障害が回復した後も，前向性および逆行性健忘は続いた。MRIの異常が不明瞭になるのに伴い，健忘も改善した。MRIの異常は，炎症と浮腫を描出し，両側の扁桃核と海馬が，健忘の責任病巣と思われた。

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 som-nolence, disorientation, amnesia, and nuchal stiffness. MRI revealed bilateral symmetrical abnormalities localized in the AM and HIPP, which showed low intensity on Tl-weighted images and high intensity on T2-weighted images. Cere-brospinal fluid examination showed a mildly evevat-ed cell count. We suspected herpes simplex virus type I encephalitis and began treatment with acy-clovir. After the patient regained a clear conscious-ness, 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.