同名半盲を呈したミトコンドリア脳筋症の1例

Homonymous hemianopsia in a case of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes（MELAS）

要約　目的：脳卒中様発作で発症し，同名半盲が続発したミトコンドリア脳筋症（MELAS）の症例の報告。

症例：25歳の女性が脳浮腫として神経内科から紹介された。8年前から感音性難聴があり，5か月前に嘔吐，複視，視野異常，てんかんがあり，5日前から同様の発作が頻発した。血液の乳酸値が高く，磁気共鳴画像検査（MRI）で右側の脳半球に高信号域があった。

所見：矯正視力は右1.0，左0.5で，眼底などに異常はなく，黄斑回避のない左側の同名半盲があった。遺伝子検査でミトコンドリア遺伝子A3243G点異常があり，MELASと診断した。以後2年間，右側の側頭葉と後頭葉の萎縮は進行し，左側の同名半盲は残存した。

結論：MELASでは，繰り返す脳卒中様発作で発症し，視野異常が続発することがある。

Abstract　Purpose: To report a case of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episode（MELAS）who showed repeated episodes simulating epilepsy followed by homonymous hemianopsia.

Case: A 25-year-old woman was referred to us from the neurology department for suspected cerebral edema. She had had hypoacusia since 8 years before. She had showed vomiting followed by diplopia, abnormal visual field and epileptic seizures since 5 months before. She showed elevated level of lactose in the blood. Magnetic resonance imaging（MRI）showed elevated signal in the right cerebral hemisphere.

Findings: Corrected visual acuity was 10 right and 0.5 left. Routine ophthalmological findings were normal. Left homonymous hemianopsia was present without macular sparing. Genetic studies showed point mutation of mitochondrial gene A3243G, leading to the diagnosis of MELAS. Atrophy of temporal and occipital lobe in the right hemisphere progressed during the following 2 years with persistent left homonymous hemianopsia.

Conclusion: The present case illustrates that repeated episodes simulating epilepsy may be the initial manifestations of MELAS followed by homonymous hemianopsia.