The unusual features of traumatic neurogenic muscular atrophy in the infant: an anatomic study.

A biopsy from the deltoid muscle of an 8-week old girl who had sustained a bilateral traumatic Erb's brachial plexus paresis at birth revealed the neurogenic atrophy to be different from that of adult muscle in that small, round fibers, similar to those observed in Werdnig-Hoffmann disease, were found. Detailed histochemistry of the fibers is submitted. On electron microscopy, there was focal degeneration of sarcomeres; a loss of myofibrils and myofilaments accompanied by increased autophagocytosis and increased amounts of glycogen; occasionally, preferential drop out of thick myofilaments and a peculiar displacement and deformation of the T-system, triads. In spite of the fact that the injury was sustained at one well defined point of time, the degree to which the muscle fibers were affected was quite variable from area to area. It is proposed that denervation in infantile muscle results in typical small rounded fibers and that this process, so different from that of adult neurogenic atrophy, is age-dependent.