筋疾患とミトコンドリア病  [in Japanese] Myopathy and Mitochondrial Disease  [in Japanese]

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Author(s)

    • 大越 教夫 Ohkoshi Norio
    • 筑波技術大学 保健科学部保健学科 Department of Health, Faculty of Health Science, Tsukuba University of Technology

Abstract

ミトコンドリア病は,ミトコンドリアDNAあるいは核DNA異常によって生じるミトコンドリアの呼吸鎖電子伝達系障害により多彩な臨床症状を来す疾患の総称である.障害されやすい臓器は,骨格筋,中枢神経系,心臓であり,特にミオパチーでは,外眼筋と四肢・体幹の骨格筋が障害されやすい.外眼筋症状はミトコンドリア病診断の重要症状の一つで,極めてゆっくり進行する眼瞼下垂と外眼筋麻痺を特徴とする.四肢の筋力低下は通常は近位筋優位であるが,遠位筋優位となることもある.また,特徴的な筋症状の一つに軽度の活動で早期から疲労をきたす運動不耐症があり,筋力低下の程度に比して強い症状として出現しやすい.進行例では嚥下障害や構音障害もみられる.早期診断のスクリーニング検査として血液・髄液の乳酸/ピルビン酸比が重要である.筋生検では,赤色ぼろ線維(ragged-red fibers)やcytochrome c oxidase欠損線維がみられる.MRI検査も重要で,脳卒中様発作を伴うミトコンドリア脳筋症(MELAS)では脳梗塞様病変,ragged-red fiberを伴うミオクローヌスてんかん(MERRF)では大脳,小脳の萎縮が特徴的である.ミトコンドリアDNAや核DNA原因遺伝子の異常を検出することが確定診断には重要となる.

Mitochondrial disease is a diverse group of disorders resulting from dysfunction of the respiratory chain, which is under the dual control of nuclear and mitochondrial DNA. The most commonly affected organ systems are muscles, the central nervous system, and the cardiac system. Mitochondrial myopathy selectively affects the extraocular muscles and/or limb and axial muscles. Ocular myopathy, which is manifested by slowly progressive ptosis and ophthalmoplegia, is an important feature in diagnosing mitochondrial disease. Limb muscle weakness is usually proximal but occasionally affects distal muscles as well. One of the most common muscular symptoms is exercise intolerance due to premature fatigue during activities. The exercise intolerance is disproportionately severe relative to muscle weakness. Bulbar muscle symptoms, such as dysphagia and dysarthria, occur in advanced cases. Serum and cerebrospinal fluid lactate and pyruvate ratios are an important screening tests for early diagnosis. Muscle biopsies typically show ragged-red fibers and cytochrome c oxidase-deficient fibers. MRI demonstrates stroke-like lesions in patients with MELAS and the atrophy of the cerebrum and cerebellum in MERRF. The identification of causative molecular defects in mitochondrial DNA and nuclear DNA enables a definitive diagnosis.

Journal

  • Neuro-Ophthalmology Japan

    Neuro-Ophthalmology Japan 31(4), 446-456, 2014

    The Japanese Neuro-Ophthalmology Society

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