A Case of Minicore Myopathy / 대한소아신경학회지

Minicore myopathy, an uncommon condition, is one of congenital myopathies. It is characterized by multifocal areas of degeneration in muscle fibers. The minicores consist of numerous small areas of decreased oxidative enzyme activity. The axis of the lesion is perpendicular or parallel to the long axis of the muscle fiber. The phenotype has been described as predominantly proximal, static or only slowly progressive muscle weakness. We report a 4 year-old-girl with respiratory failure, thoracic scoliosis, hypotonia and facial weakness, who was diagnosed as minicore myopathy by muscle biopsy. The laboratory investigations, such as creatine phosphokinase and lactic dehydrogenase levels, and the nerve conduction velocity were normal. The muscle biopsy showed marked size variations of myofibers, marked endomyseal and perimyseal fibrosis, and moderate fatty changes in myofibers. The histochemical studies showed multiple focal losses of mitochondria. These findings are consistent with minicore type congenital myopathy.

Multicore myopathy

Multicore myopathy is a rare congenital myopathy. The multicores consist of numerous small areas of decreased oxidative enzyme activity. The long axis of the lesion is perpendicular or parallel to the long axis of the muscle fiber. These cores are usually smaller than central cores. For this reason they are also called minicores. Although the multicores represent a nonspecific change in that they can be observed in malignant hyperthermia, muscular dystrophy, inflammatory myopathy, etc. Muscular weakness dating from early infancy is combined large proportion of the muscle fibers. In about half of the reported cases the muscular weakness has not been progressive, while in the others a slow progression has occurred. This 9-year-old boy presented with congenital nonprogressive myopathy associated with thoracic scoliosis and bilateral equinovarus deformity. The serum creatine phosphokinase and lactic dehydrogenase levels were normal. Electromyography showed "myopathic" features. The biopsy revealed a marked size variation in myofibers, ranging from 10 microns to 100 microns. A few small angular fibers and slight endomyseal fibrosis were also noted. There was type I fiber predominance. NADH-TR reaction disclosed more well-defined cores with loss of intermyofibrillary mitochondrial activity. These cores were usually located with loss of intermyofibrillary mitochondrial activity. These cores were usually located in the peripheral portions of the myofibers and the core size measured 10-30 microns in diameter. Electron microscopic examination revealed circumscribed areas of disintegrated Z band material and disorganized sarcomeric units near the sarcolemma. A decrease in the number of mitochondria and glycogen particles was noted.