Abstract: Objective To study the clinical features and sigificance of systemic lupus erythematosus(SLE) patients associated with myositis. Methods A comparative study of 64 cases of systemic lupus erythematosus (SLE) associated with myositis and 43 cases of dermatomyositis(DM) was carried out by the observation of clinical features,serum levels of muscle enzymes,electromyographic pattern and muscle biopsies. Results The results showed there were 35.5% of patients with SLE associated with myositis The myositis symptoms,muscle weakness and atrophy in these patients were less significant than those of DM (P<0.01). The abnormal esophageal motility was not seen in these patients. Although the serum level of muscle enzymes in SLE patients with myositis was elevated,the level was significantly lower than that of DM patients(P<0.01). Electromyographic abnormality accounted for 74.4%(32/43) of SLE patients with muscle involvement,and the difference was not significant from that of DM patients (P>0.05). Muscle biopsy showed that there were obvious interstitial vasculitis with infiltration of lymphocytes and histiocytes,focal swelling and homogeneous degeneration of mucscle fibers,and no necrosis fragmentation was observed. Conclusion SLE myositis has its distinct clinical and pathological characteristics which are different from those of DM.

Key words: Lupus erythematosis,systemic, Dermatomyositis