視野障害を発症し改善した小児型ミトコンドリア脳筋症の1例

A case of pediatric mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes（MELAS）with visual field impairment

要約　目的：視野障害を発症し，L-アルギニン，タウリンを含むミトコンドリアカクテルビタミン療法が奏効した小児型ミトコンドリア脳筋症（MELAS）の症例報告。

症例：10歳，女児。2年前より特別支援学級に転籍。2週間前に頭痛，全身倦怠感があり，頭痛の増悪を認めたため近医を受診した。頭部単純CTで左後頭葉に低吸収域を認め，また右方が見えにくいとの訴えもあり，精査目的で東海大学医学部付属病院眼科に紹介され受診となった。

所見：矯正視力は両眼とも1.2で，前眼部，中間透光体，眼底に異常はなかったが，視野検査で右同名半盲を認めた。頭部単純MRIで左側頭葉から後頭葉に血管支配領域と一致しない異常信号と，MRスペクトロスコピーで異常所見を呈した部分に一致して乳酸ピークの上昇を認めた。また血液検査で乳酸値の上昇がみられ，さらにミトコンドリア遺伝子検査でA3243G点変異を認めたことからMELASと診断された。ミトコンドリアカクテルビタミン，およびL-アルギニン，タウリン内服加療を開始し，全身症状および頭部MRI所見の改善を認め，右同名半盲も完全に消退した。

結論：視野障害を含めた症状の改善が得られた小児型MELASを経験した。小児型MELASでは成人型に比べて今後重症化する可能性も高く，注意深い経過観察を要する。

Abstract　Purpose：To present a case report of pediatric mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes（MELAS）with visual field impairment and successful mitochondrial cocktail therapy comprising L-arginine and taurine.

Case：A 10-year-old girl, presented headache and general malaise two week ago. Simple head computed tomography（CT）revealed a low absorption zone in the left occipital lobe. She also had a right visual field defect, and was subsequently referred to our hospital.

Findings：The best corrected visual acuity was 1.2 in both eyes, with no remarkable findings. Goldmann perimetry confirmed right homonymous hemianopia. Magnetic resonance imaging（MRI）revealed a contrast mismatch between the intensity at the vascular and innervation region in the left temporal and occipital lobes. MR spectroscopy revealed a lactate peak consistent with the abnormal intensity. Laboratory data showed an increase in the lactic acid level, and mitochondrial genetic testing showed an A3243G point mutation. The patient was diagnosed with MELAS. Several supplementations, including vitamins, L-arginine, and taurine, were induced in the mitochondrial cocktail treatment. Notable improvement was observed in the patient's symptoms, MRI findings, and the right visual field defect.

Conclusions：We encountered a case of pediatric MELAS with improved right visual field defect. Pediatric type MELAS is may manifest with more severe symptoms than the adult type. Hence, careful follow-up is necessary.