HMGB1 and polymyositis: Serum levels of HMGB1 in patients with PM were 12.75 ng/ml (4.34–25.07 ng/ml), and those in DM were 20.75 ng/ml (3.80–124.88 ng/ml), while those in healthy controls were 5.64 ng/ml (2.71–8.71 ng/ml).