Electron microscopy of muscle biopsy and nerve pathology. A: Pigment granules in the cytoplasm of histiocytes. B: Isolated pigment granule in the subsarcolemmal cytoplasm. C: Pigment granules form a small cluster in a myofiber. D, E: Autophagic vacuoles (pink arrowhead) in association with numerous pigment granule clusters (blue arrowhead). F: Light microscopy of the sural nerve specimen shows a reduction in the number of large-diameter myelinated fibers. G: Electron microscopy of the sural nerve specimen shows electron-dense granules in the cytoplasm of a Schwann cell, where the myelin sheath is disrupted.