Image 1 of 4 Mitochondrial myopathy. There is an increased number of mitochondria in the subsarcolemmal space. They also contain paracrystalline inclusions. The muscle fibers with this mitochondria accumulation are seen in light microscopy with the Masson trichrome stain as "ragged red fibers."

Image 2 of 4 Mitochondrial myopathy. In mytochondrial myopathies, ultrastructural appearances range from large, subsarcolemmal accumulations of mitochondria (as seen here) to fibers containing disordered myofibrils, degenerating mitochondria and vacuoles. The abnormal mitochondria most of the time can be identified by their paracrystalline inclusions. Mitochondria in these accumulations are sometimes found together with lipid droplets.