ノカルジア感染による結膜下膿瘍の臨床的特徴

Clinical features of subconjunctival abscess by Nocardia infection

要約　目的：治療に難渋したノカルジア感染による結膜下膿瘍の2例を報告し，その臨床的特徴を検討する。

症例1：76歳，女性。左鼻涙管閉塞の既往があった。2か月前から左眼充血で近医にてレボフロキサシン点眼とステロイド点眼で加療されていたが悪化し，当院へ紹介された。左鼻側に結膜下膿瘍と周辺部角膜潰瘍を認めた。自壊膿の塗抹鏡検から放線菌が検出された。膿瘍部では強膜壊死によるぶどう膜露出を認めたため，角膜菲薄部も含め表層角膜移植を行った。質量分析によりNocardia novaと同定されたため，抗菌薬点眼に加え，ST合剤内服，シクロスポリン内服にて約3か月で消炎を得た。その後，涙管チューブ挿入術を行い，完治した。

症例2：71歳，女性。右黄斑浮腫に対しトリアムシノロンアセトニドのテノン囊下注射を近医で受けた2か月後に充血をきたし，レボフロキサシン点眼とステロイド点眼で改善せず，当院へ紹介された。右鼻下側に結膜下膿瘍を認め，自壊膿の塗抹鏡検から放線菌が検出され，16S rRNA遺伝子解析でNocardia aobensisと判明した。MRIで結膜下膿瘍に続く眼窩膿瘍が認められ，スルバクタム/アンピシリンの全身投与とテノン囊下注射，トブラマイシン点眼で寛解・増悪を繰り返し，約9か月で消炎を得た。

結論：涙道閉塞やテノン囊下注射後に生じた難治性の隆起性結膜病変では，ノカルジア感染の鑑別が必要である。早期診断には排膿物の塗抹鏡検・培養検査が重要である。

Abstract　Purpose：We report two cases of subconjunctival abscesses caused by Nocardia infection that were difficult to treat and review their clinical features.

Case 1：A 76-year-old woman with left nasolacrimal duct obstruction was referred to our hospital for worsening hyperemia in the left eye despite two months of treatment with levofloxacin and steroid eye drops. A subconjunctival abscess and peri-corneal ulcer were observed on the nasal side of the left eye, and actinomycetes were detected on smear examination of the self-destructing pus. In the abscess area, uveal exposure due to scleral necrosis was observed, and superficial corneal transplantation including corneal thinning, was performed. Using mass spectrometry, we identified Nocardia nova. The patient was treated with oral sulfamethoxazole-trimethoprim and cyclosporine in addition to antimicrobial eye drops, and the inflammation disappeared in about 3 months. She underwent lacrimal duct tube insertion for nasolacrimal duct obstruction and made a complete recovery.

Case 2：A 71-year-old woman developed hyperemia two months after receiving sub-Tenon triamcinolone acetonide injection for macular edema in the right eye. She was referred to our hospital as she showed no improvement with levofloxacin and steroid eye drops. A subconjunctival abscess was found in the inferior nasal region, and actinomycetes were detected on smear examination of the self-destructing pus. Using 16S rRNA gene sequence analysis, we identified Nocardia aobensis. MRI showed a subconjunctival abscess followed by an orbital abscess. Systemic administration and sub-Tenon injection of sulbactam/ampicillin and tobramycin eye drops were performed, with repeated remissions and exacerbations. The inflammation disappeared in about 9 months.

Conclusions：Nocardia infection should be differentiated in refractory elevated conjunctival lesions arising with lacrimal canal obstruction or after sub-Tenon steroid injection. Smears and cultures of pus are important for early diagnosis.