炎症反応を伴った進行性多巣性白質脳症—免疫不全の原因の多様性と病理所見

Progressive Multifocal Leukoencephalopathy with Inflammatory Reactions

進行性多巣性白質脳症（PML）は，宿主の免疫低下に伴いJCウイルスが再活性化して起こる脱髄脳症である。臨床的に免疫低下の原因が不明瞭で，髄液ポリメラーゼ連鎖反応（PCR）でウイルス陰性でもなお，画像上PMLの可能性を否定できず脳生検を施行する場合がある。こうした症例では，病理診断の指標となる典型的な核内ウイルス封入体を有する細胞に乏しく，高度な炎症細胞浸潤を伴う場合がある。JCウイルスに対する宿主免疫応答が保たれている状態と考えられ，予後は良好である。本稿では，炎症反応を伴ったPMLについて，近年問題となっている免疫再構築症候群も含め，概説する。

Abstract

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disorder caused by reactivation of the JC virus associated with impaired host immunity. However, PML may occur even without an evident cause of immunosuppression. In such cases, JC virus DNA in cerebrospinal fluid (CSF) may not be detectable with polymerase chain reactions (PCR), and a brain biopsy may be performed. Pathology may exhibit marked inflammatory reactions around the JC virus-infected cells, although typical intranuclear viral inclusions would rarely be seen. Atypical inflammation in patients with PML likely an indication of the host's immune-response against the virus. this is usually observed in those with relatively-mild immunosuppression with favorable prognosis. Here, we describe cases of PML that exhibited inflammatory reactions; a recent topic, PML with immune reconstruction inflammatory syndrome (IRIS), will also be discussed.

—(Received September 9, 2015; Accepted September 24, 2015; Published April 1, 2016)