Objective: To describe clinical and paraclinical characteristics of muscular lesions in patients with dermatomyositis. Subjects: 41 dermatomyositis patients, diagnosed by 1995 Tanimoto criteria, hospitalized in Rheumatology Department, Bach Mai hospital from May 2008 to October 2011. Methods: A cross-sectional description study. Results: The most common positions of muscular lesion were muscles of limbs (97.56 percent), main characteristics was symmetrical proximal muscle weakness (97.56 percent)
difficulty in rising from a sitting position was observed in 97.56 percent cases. The average concentration of serum CK was 4151.25 + or - 1355.4 U/I, serum SGOT was 136.32 + or - 26.13 IU/l and serum SGPT was 107.76 + or - 47.30 IU/l. 80 percent patients had abnormality in electromyography, the most common sign was increased insertional activity (70 percent). 92.31 percent patients had histopathological changes in muscle biopsy, including degeneration of muscle (66.7 percent) and infiltration of inflammatory cells (59 percent). Conclusions: The muscle manifestations in dermatomyositis (in combination with dermatological lesion) were characterised by lesion of limb muscles, especially lower limb muscles, with symmetrical proximal muscle weakness, elevated serum CK and transaminase, abnormality of electromyography (increased insertional activity) and degeneration of muscle and infiltration of inflammatory cells in muscle biopsy.