To investigate whether the combined initial treatment of glucocorticoids and tacrolimus is superior to glucocorticoids alone in PM/DM-IP patients, we conducted a multicenter clinical trial to evaluate the efficacy and safety of a combination treatment of glucocorticoids and tacrolimus for 1 year in patients with newly developed active PM/DM-IP or its relapse by comparing against clinical outcome of historical control patients who were treated with glucocorticoid alone as an initial treatment.