Myopathy and Mitochondrial Disease

DOI
  • Ohkoshi Norio
    Department of Health, Faculty of Health Science, Tsukuba University of Technology
  • Ishii Akiko
    Department of Neurology, Faculty of Medicine, University of Tsukuba

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  • 筋疾患とミトコンドリア病

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Description

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.

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