IFIH1 and Arthritis: When clinical characteristics were compared between DM patients with and without anti-MDA5 antibodies, 55 patients positive for anti-MDA5 antibodies represented younger disease onset (P = 0.01); higher frequency of CADM (P < 0.0001), ILD (P < 0.0001), RP-ILD (P < 0.0001), arthritis (P < 0.0001), and fever (P = 0.0002); and lower frequency of classic DM (P < 0.0001), chronic ILD (P = 0.002), and malignancy (P = 0.0005), compared with 117 negative for anti-MDA5 antibodies.