Ultrastructural pathology of skeletal muscle in systemic lupus erythematosus.

Muscle biopsies from 12 patients with systemic lupus erythematosus (SLE) who presented with muscle weakness and myalgias were studied ultrastructurally. Two different alterations were present, myositis (11 cases), and vacuolar myopathy (1 case). The myositis exhibited muscle atrophy, microtubular inclusions, and a mononuclear cell infiltration. In one case, with increased serum creatine phosphokinase, fiber necrosis was evident. Capillary abnormalities included thickening and reduplication of basement membrane, alterations of endothelium and microtubular inclusions. The vacuolar myopathy also showed vacuolated muscle fibers and occasional zebra bodies. The different associations between muscle diseases and SLE are grouped. Our data suggest that SLE myositis is a distinct clinical and pathological entity. The SLE vacuolar myopathy is a pathological entity clinically undistinguishable from SLE myositis.