RESUMO
Mitochondrial myopathy (MM) has been applied to muscle disease in which mitochondria have abnormal structure, function or both. To characterize the pathologic findings of MM, we examined the ultrastructural and histochemical findings of 24 cases of MM. The ultrastructures of the MM were characterized by abnormal mitochondria in number (pleoconia) and size (megaconia), and showed predominant accumulation of mitochondria in the subsarcolemmal space of myofibers in all cases. Mitochondria contained abnormally shaped cristae (concentric form and gyriform) in 79% of cases. Paracrystalline inclusion which was known to be a characteristics of MM were seen only in 7 cases (29%). Electron dense deposits were more frequently found (77%) in abnormal mitochondria of chronic progressive external opthalmoplegia and Kearn-Sayre syndrome. But, other findings were not specific for the specific clinical entities. On succinate dehydrogenase (SDH) stain, ragged red fibers (RRF) showed more intense positivity than modified Gomori-trichrome stain and definite strong reactive products were present along the periphery of myofibers which showed normal findings on modified Gomori-trichrome stain. In conclusion, ultrastructural findings such as mitochondria showing pleoconia with megaconia, and bizarre shaped cristae may be helpful for the diagnosis of MM and SDH stain is more useful for identification of RRF than modified Gomori-trichrome stains.