Origin of the ring muscle fibers in neuromuscular diseases.

Morphological histochemical and ultrastructural examination of the ring fibers in one case of myotonic dystrophy and one case of mitochondrial myopathy provides evidence that the ring fibers develop in the course of fiber splitting and reinnervation of muscle fiber fragments. The reinnervation may have been due to a neurogenic lesion coexisting in both cases with the myopathic picture. The histologically different type of annular myofibrils observed in one case of cap disease is probably due to delayed embryonic development and abnormal relations between the myofibrils and elements of the cytoskeleton.