Relationship between capillary and muscle damage in dermatomyositis.

To assess the pathogenetic importance of capillary damage and its relationship with degenerating muscle fibers in dermatomyositis (DM), an electron microscope study of eight muscle biopsy specimens (adult and juvenile forms) and seven muscle specimens from patients with other neuromuscular diseases was conducted. There was a 49% reduction of capillaries in the muscle specimens of DM patients. Capillary damage also was more frequent in the DM group than in control group (p less than 0.001). We found a striking relation between capillary and muscle damage in the DM group (p less than 0.002) but not in the control group. The diagnostic value of undulating tubules within endothelial cells is also discussed.