[Ultrastructure of skeletal muscles in children with dermatomyositis]

The ultrastructure of skeletal muscles was studied on 6 bioptates collected from children with the idiopathic form of dermatomyositis. The main type of the affection of muscle fibers was myolysis the intensity of which correlated with the degree of activity of the disease. In focal myolysis, signs of intracellular regeneration were found in fibers. Diffuse myolysis was characterized by retained hypertrophic nuclei and basal membranes of sarcolemma against the background of complete degeneration of myofibrillae and a sharp decrease in the fiber diameter. Considerable hyperplastic changes in myosatellitocytes were found, but with no regenerating fibers, however. The permanent features included hypertrophic and dystrophic changes in the vascular endothelium and pericytes. In the maximally active disease, destruction of capillaries and a decrease in their numbers were found. Microtubular structures and nuclear bodies were found in the endothelium, pericytes, and less frequently in other cells.