Abstract
An 8-year-old male Japanese Shiba exhibited muscle wasting and a stiff gait. A low-amplitude myotonic discharge was recorded by needle electromyography (EMG). A histopathological examination on a tru-cut biopsy sample from the muscle revealed myofiber size variations. Internal nuclei and cytoplasmic vacuoles were observed in many fibers. A type 1 fiber predominance and many hybrid type fibers were observed immunohistochemically. On the basis of these EMG and histopathological findings, myotonic dystrophy (DM) was suspected as tentative diagnosis. The cytoplasm around the vacuoles was immunopositive for cytochrome c, tom 20, and SOD-1, suggesting that these vacuoles might occur within mitochondria. Collectively, these results indicate that a mitochondrial abnormality partly play the role on the pathogenesis of present case.