質量分析法にてNocardia veterana角膜炎と診断された1例

The retrospective analysis of clinical cases with corneal injuries secondary to a case diagnosed with Nocardia veterana keratitis by mass spectrometry

要約　目的：質量分析法（MALDI-TOF MS）にてNocardia veterana角膜炎と診断された1例を報告する。

症例：78歳，男性。濾胞性リンパ腫に対してレナリドミドとリツキシマブで治療され，安定していた。7か月前に左眼の視力低下，異物感を自覚し近医を受診した。ヘルペス角膜炎と診断され，アシクロビル眼軟膏が開始されたが改善がみられず，4か月後に近医へ紹介となった。バラシクロビル内服，ベタメタゾン点眼，プレドニゾロン50mg内服を追加したが眼所見は改善せず，当院へ紹介となった。当院初診時の左視力は指数弁で，左角膜の実質浅層に特徴的な花弁様の白色沈着を認め，前房炎症と前房蓄膿も認められた。角膜感染を疑い角膜擦過物の検鏡と培養検査を施行し，グラム陽性桿菌が検出され，ガチフロキサシン点眼，セフメノキシム点眼，エリスロマイシン・コリスチン眼軟膏を開始したところ，感染巣の縮小と前房蓄膿の消失がみられ，自覚症状も改善した。培養検査および質量分析法にて原因菌はN. veteranaと同定され，薬剤感受性試験ではニューキノロン系抗菌薬に高度耐性を認めた。

結論：N. veteranaは，免疫不全患者において呼吸器感染症を引き起こすことが報告されているが，角膜炎を起こした症例は本邦では報告はない。本症例では角膜擦過物の検鏡と培養検査に加え，質量分析法を行うことが原因菌の同定に有用であった。

Abstract　Purpose：To report a case of Nocardia veterana keratitis identified by the causative organism（MALDI-TOF MS）.

Case：A 78-year-old man with follicular lymphoma was treated with lenalidomide and rituximab and was stable. Since 7 months, he had become aware of his left eye vision loss and foreign body sensation and consulted a nearby doctor. He was diagnosed with herpes keratitis and started aciclovir eye ointment, but no improvement was seen and he was referred to another nearby doctor four months later. He added valacyclovir, betamethasone, and prednisolone 50 mg, but his ocular findings did not improve and he was referred to our hospital. At the time of referral, the visual acuity of the left eye was counting finger, and petal-like white deposits characteristic of the parenchymal superficial layer of the left cornea were observed. Anterior chamber inflammation and hypopion were also observed. Suspected corneal infection, corneal scraping and culture examination were performed, and Gram-positive bacilli were detected, and gatifloxacin eye drops, cefmenoxime eye drops, and erythromycin/colistin eye ointment were started. Symptoms also improved. N. veterana was identified via culture testing and mass spectrometry, and was highly resistant to new quinolone antibiotics in drug susceptibility testing.

Conclusions：N. veterana has been reported to cause respiratory infections in immunocompromised patients, but no cases of keratitis have been reported in Japan. In this case, mass spectrometry was useful for identifying the causative organism in addition to the microscopic examination and culture examination of the corneal scrapes.