Serum levels of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) in patients with polymyositis (PM)/dermatomyositis (DM) and in healthy controls. Serum TWEAK levels were determined by a specific ELISA. TWEAK levels in healthy subjects were compared to patienta with PM or DM (A). There was no statistical difference in serum TWEAK levels between patients previously untreated and patients who received treatments (B). No significant differences were observed when TWEAK levels were compared in patients with PM/DM sub-grouped based on antinuclear antibody (ANA) positivity (C), Jo-1 positivity (D), presence of interstitial lung disease (ILD) (E) and presence of oropharyngeal dysphagia (F). Correlation of serum levels of TWEAK with myositis disease activity assessment visual analog scales (MYOACT) global disease activity (G) and MYOACT muscle disease activity (H) were analyzed. Twelve newly diagnosed PM/DM patients had significantly decreased MYOACT global disease scores after treatment (I), however, no significant difference was observed in the patients’ serum TWEAK levels before and after treatment (J). Serum CD163 levels were determined by a quantitative ELISA. Serum CD163 levels were significantly higher in PM/DM patients compared to healthy controls (K), and serum CD163 levels were found to be negatively correlated with serum TWEAK levels in PM/DM patients (L). The data for unpaired samples were analyzed by using the Mann-Whitney U-test. Spearman’s correlation analysis was used to test for correlation. The Wilcoxon signed rank test was used on paired data. Horizontal bars indicate median levels.