Abstract: AIM: To study the difference of clinical charactertics between polymyositis and dermatomyositis patients.METHODS: 11 cases of polymyositis and 21 cases of dermatomyositis were included in this study.Their muscle strength, serum creatine phosphokinase (CPK) levels, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), hospitalization times, the quadriceps muscle MRI and high-resolution lung CT (HRCT) were compared.RESULTS: There were no statistic differences among muscle strength, ESR, CRP, hospitalization times, hoarseness and dysphagia in the two groups(P>0.05).The level of CPK in polymyositis patients was significantly higher than that in dermatomyositis patients [(3032±2973)vs(390±947) U/L(P=0.015)]. But the rate of incidence of interstitial pneumoniin in dermatomyositis patients was significantly higher than that in polymyositis patients (P=0.021),and the therapy effect of glucocorticoids in polymyositis patients was significantly better than that in dermatomyositis patients (P=0.013). 4 deaths were all dermatomyositis patients,3 cases died with interstitial pneumoniin developed respiratory failure and 1 cases died with rhabdomyolysis developed acute renal failure.CONCLUSION: The level of CPK in dermatomyositis patients is higher than polymyositis patients, but more complicated that in by interstitial pneumoniin and poor prognosis.

Key words: Polymyositis, Ermatomyositis, Prognosis