OBJECTIVETo investigate the expression of C5b-9 in the skeletal muscle blood vessels in patients with necrotizing myopathy and explore its role in the pathogenesis of this disease.

METHODSThe expression of C5b-9 and MHC-I in the skeletal muscular fibers and blood vessels in 4 patients with necrotizing myopathy was detected using enzymohistochemistry and immunohistochemistry.

RESULTSFocal or dispersive necrotic muscle fibers with obvious phagocytosis were observed in all the 4 patients. No inflammatory cell infiltration was found in the perimysium or perivascular regions. HE staining showed a decreased number of local small blood vessels, and the some small blood vessels showed thickened vascular walls. Immunohistochemistry detected prominent C5b-9 expression in the necrotic muscle fibers and the blood vessels, and diffuse strong C5b-9 expression was found in the vascular walls, vascular endothelial cells and the smooth muscle layer. No MHC-I deposition was detected in the muscular fibers and blood vessels.

CONCLUSIONC5b-9 contributes to the pathogenesis of necrotizing myopathy mediated by pathologies in the blood vessels.