非ヘルペス性急性辺縁系脳炎

Non-herpetic acute limbic encephalitis

　非ヘルペス性急性辺縁系脳炎（ALE）は両側海馬・扁桃体などにMRI異常を示し，ウイルス学的にherpes simplex virus（HSV）-1，-2感染が否定される急性脳炎であるが，約50例の報告例が集積されている。一方，骨髄移植などに伴ったHHV-6の再活性化による急性辺縁系脳炎，自己免疫疾患に伴う辺縁系脳炎などの類縁疾患群が報告されてきた。様々なウイルス感染，自己免疫疾患などを引き金とした感染・免疫学的機序を成因とする考え方が有力である。MRIで両側海馬病変を示したヘルペス脳炎例で，併せて肺小細胞癌を合併した症例を呈示し，ALE，ヘルペス脳炎，傍腫瘍性辺縁系脳炎の関連について言及し，ALEをめぐる問題点，関与するウイルス感染などに関し考察を加えた。

　Non-herpetic acute limbic encephalitis（ALE）is characterized by MRI abnormalities in the bilateral hippocampi and amygdalae, and negative polymerase chain reaction（PCR）for herpes simplex virus（HSV）in the cerebrospinal fluid（CSF）and negative enzyme-linked immunosorbent assay（ELISA or EIA）antibodies for HSV-1 and-2 in the serum and CSF. Approximately 50 patients with non-herpetic ALE have been reported in Japan, meanwhile several patients with human herpesvirus（HHV）-6 limbic encephalitis（LE）after stem cell transplantation or LE in association with autoimmune diseases have been described. To date, the causative agent of ALE has not been identified, and the pathogenesis of ALE may be caused by mild infections and immunological process following various viral infections, autoimmune diseases, and so on. An important case of herpes simplex encephalitis（HSE）presenting with bilateral hippocampal lesions on MRI, and simultaneously complicated by small cell lung carcinoma was briefly described, and tentative relationships among ALE, HSE, and paraneoplastic LE were discussed. Several problems around ALE were also mentioned.