Congenital myopathy with focal loss of cross striations: a case report with morphologic and immunohistochemical study.

A case of an unusual congenital myopathy is reported. The boy presented at birth with generalized muscular hypotonia and dysmorphic features. Muscle biopsy at the age of 10 years revealed focal areas with decreased ATPase activity and variable oxidative enzyme activity. There was only one type II fiber in the whole section. 22.5% of fibers had central nuclei, sometimes with radial arrangement of the intermyofibrillary network. Focal lesions displayed strong desmin and weak vimentin immunoreactivity. On electron microscopic examination normal sarcomeres were focally disrupted and mitochondria were absent from these areas; the normal structure was replaced by numerous fragments of sarcoplasmic reticulum, filamentous material, scattered glycogen particles, and the Z-line was replaced by irregular longitudinal streaks of electron-dense fibrillar material. We classify this case as a congenital myopathy with focal loss of cross striations.