Ragged-red muscle fibers Ragged-red fibers UMLS:C3275417 Ragged-red fibres An abnormal appearance of muscle fibers observed on muscle biopsy. Ragged red fibers can be visualized with Gomori trichrome staining as irregular and intensely red subsarcolemmal zones, whereas the normal myofibrils are green. The margins of affect fibers appear red and ragged. The ragged-red is due to the accumulation of abnormal mitochondria below the plasma membrane of the muscle fiber, leading to the appearance of a red rim and speckled sarcoplasm. HP:0009076 Mitochondrial proliferation in muscle tissue Ragged red muscle fibres Ragged-red muscle fibres This finding is demonstrated by muscle biopsy. Note that additionally, muscle fibers with mitochondrial proliferation stain darkly for succinic dehydrogenase (SDH). Ragged red muscle fibers HP:0003200 Abnormal muscle fiber morphology