Patterns of neuromuscular disease. As related to stages of normal embryogenesis in voluntary muscle.

Skeletal muscle samples from the upper and lower extremities of 38 human fetuses (6 to 18 weeks' gestation) of both sexes were studied by histologic, histochemical, and electron microscopic methods. Ultrastructural morphometry was applied. In the different stages of normal development are found regressive changes, ranging from reversible dystrophic to irreversible necrotic alterations, which are characteristic of either primary myogenic myopathies or primary neurogenic muscle atrophies in older age. Several pathologic patterns of so-called congenital myopathies also presented. On the basis of their findings, the authors conclude that in a certain group of congenital myopathies full normal development of muscle is hindered or blocked and that groups of muscles or the whole voluntary musculature is arrested at certain stages of maturation. For example, insufficient or absent innervation of the fetal muscle may be a factor in Werdnig-Hoffmann or Kugelberg-Welander syndromes. The authors' findings suggest that pathologic patterns in muscle diseases have been used physiologically in fetal development to eliminate unnecessary overproduction of muscle fibers.