MRIで髄膜造影を呈し脳生検で診断した脳アミロイドβ関連血管炎の1例

Amyloid Beta-Related Angiitis: Brain Lesions Showing Leptomeningeal Gadolinium Enhancement on MRI and Characteristic Surgical Pathologic Features

はじめに

　原発性中枢神経系血管炎［primary angiitis of the central nervous system（CNS）：PACNS］は全身の血管炎を伴わずに，中枢神経系の中小血管に炎症をきたす原因不明の疾患である。臨床症状は極めてバリエーションに富み，多巣性の症候と階段状の症状進行を示す。脳生検を行い，病理組織学的に血管周囲リンパ球浸潤，肉芽腫性変化や血管壁のフィブリノイド壊死所見が得られれば診断できるが，剖検によってはじめて診断されることも多い¹⁾。

　近年，PACNSの一部の症例では中枢神経系の血管壁にアミロイドβの沈着がみられ，アミロイドβに対する免疫反応が惹起されることによって肉芽腫性変化を伴う血管炎を生じている可能性が示唆され，アミロイドβ関連血管炎（amyloid β-related angiitis：ABRA）の疾患概念が確立しつつある²⁾。今回，頭部MRIで髄膜造影効果を呈したものの，臨床所見や各種検査所見からは疾患特異的異常が得られず，脳生検によりくも膜下腔の血管にアミロイドβの沈着を伴う血管炎や肉芽腫性変化を認め，ABRAと診断した1例を経験したので報告する。

Abstract

　Amyloid-β-related angiitis (ABRA) of the CNS occurs in association with vasculitis of small-and medium-sized leptomeningeal arteries. Here, we describe the clinicopathological features of a 76-year-old man with ABRA. The patient suffered progressive truncal oscillation, aphasia, and recent memory disturbance with a subacute disease onset. His cerebrospinal fluid showed a mild increase in protein levels (101 mg/dL) and pleocytosis (8/mm³). High-intensity brain lesion were detected on T₂-weighted and FLAIR MRI scans, and prominent spread of gadolinium enhancement spreading was observed through the sulci of the left occipital and temporal lobes and left cerebellar hemisphere. A biopsy of the left temporal lesion showed a granulomatous and angiodestructive inflammation with infiltration of many CD4⁺ T-lymphocytes and multinucleated giant cells and with fibrinoid necrosis of the arterial walls in the subarachnoid space. Immunolabeling for Aβ_1-40 revealed the abundant deposition of this protein in the affected arteries. On the basic of the diagnosis of ABRA, immunosuppressive therapy was conducted, and it ameliorated the clinical course.

(Received: September 18, 2012, Accepted: November 28, 2012)