孤発性Actinomyces脳膿瘍の66歳女性例

Solitary Actinomycotic Brain Abscess: Case Report

はじめに

　ActinomycesはNocardia，Streptomycesと同様に菌糸形成菌に分類されるグラム陽性桿菌である。非好酸性の嫌気性菌であり，ヒトに病原性を有するものは主としてActinomyces israeliiとされ，頭頸部，胸腹部に好発する¹⁾。中枢神経感染症を呈するのは稀である^2-5)。また，その場合でも全身の先行感染があり，そこからの二次性の感染であることが大部分である。感染は緩徐で発熱・炎症所見に乏しいことも多く，占拠性病変としての症状が多い。渉猟しえた範囲では本邦での脳膿瘍の報告は見当たらなかった。

　今回筆者らは，中枢神経のみの感染巣で診断・治療に苦慮したActinomyces脳膿瘍を経験した。同じアクチノミセス目の中で好気性のNocardiaとは類似点も多々あるが，治療法が異なるので両者を鑑別するのは非常に重要である。両者の類似点と相違点を中心に文献的考察を加えて報告する。

Abstract

　Actinomycotic brain abscess is a rare condition with uncertain clinical features. Here we report the case of a 66-year-old immune-competent woman with an actinomycotic brain abscess who presented with sensory aphasia and mild right hemiparesis. She had no febrile episode or headache. Moreover, she did not have any periodontal or oto-rhino-laryngological disease, and the results of laboratory tests were normal. A computed tomography scan showed an irregular, low-density area in the left parietal lobe. Subsequent magnetic resonance imaging showed low-signal intensity in a T₁ weighted image, high-signal intensity in a T₂ weighted image, and mixed intensity on a diffusion weighted image. Thallium-201 chloride scintigraphy showed definite accumulation of thallium in the lesion and the patient's condition gradually deteriorated. Ten days after gadolinium administration, a T₁ weighted image showed a multi- lobulated irregular mass in the left parietal lobe. The patient subsequently underwent craniotomy and evacuation of the yellowish abscess. Gram staining of the tissue showed the presence of gram-positive filamentous rods, and abscess cultures were positive for Actinomyces and Prevotella disiens. The abscess resolved after treatment with a high dose of intravenous penicillin G (24 million units/day) for 8 weeks, followed by an oral dose of amoxicillin for 4 months. The patient was discharged with a rudimentary limitation of the visual field.

（Received: October 20,2011,Accepted: December 28,2011)