ミトコンドリア脳筋症・乳酸アシドーシス・脳卒中様発作症候群（MELAS）

Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like Episodes（MELAS）

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・ミトコンドリア脳筋症・乳酸アシドーシス・脳卒中様発作症候群（MELAS）はミトコンドリア病の中で最も頻度の高い臨床病型であり，20歳以下での発症が多い．臨床症状は多様で，脳卒中様発作，痙攣，頭痛の頻度が高い．

・CT/MRIでは後頭頭頂葉，側頭葉後部に好発する血管支配域に一致しない梗塞様病変を示し，急性期は血流亢進を示すことが多い．MRSでの著明な乳酸ピークは，中枢神経系への乳酸蓄積を示す重要な所見である．

　Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes（MELAS）is the most dominant form of mitochondrial diseases, presenting with headaches, seizures, and stroke-like episodes. Stroke-like episodes is a distinguishing feature of MELAS. Symptoms appear before the age of 20 years in 65-76% of patients. For the clinical diagnosis of MELAS, evidence of lactate accumulation in the central nervous system is important.

　The radiographic features of MELAS are stroke-like lesions in the affected brain areas, primarily the occipito-parietal or posterior temporal lobe. MRI shows high signal intensities on T2-weighted or FLAIR images. The cerebral blood flow in lesions can be increased in the acute phase. MR spectroscopy（MRS）shows a lactate peak in the brain lesions, which is important evidence of lactate accumulation. In pediatric or young adult patients with occipito-parietal stroke-like lesions, a prominent lactate peak in MRS is the key radiographic sign that supports the diagnosis of MELAS.