Elevated serum levels of manganese superoxide dismutase in polymyositis and dermatomyositis

We studied serum concentrations of manganese superoxide dismutase (Mn SOD) and copper-zinc superoxide dismutase (Cu/Zn SOD) in 22 patients with polymyositis and dermatomyositis (PM/DM), 87 patients with four types of muscular dystrophy, 20 patients with amyotrophic lateral sclerosis, and 15 patients with collagen vascular diseases (CVD). Serum levels of Mn SOD were increased only in the patients with PM/DM and CVD, and the elevation was more prominent in those with PM/DM. Levels of Cu/Zn SOD were slightly elevated in some patients with PM/DM and Duchenne muscular dystrophy. In patients with PM/DM, the change in Mn SOD levels corresponded to disease activity as closely as or more closely than those of creatine kinase. The results indicate that serum Mn SOD may be a useful clinical marker for PM/DM.