IFIH1 and pulmonary fibrosis: When the disease activity of cADM recurred (before recommencing PSL), the serum levels of ferritin, LDH, Krebs von den Lungen-6 (KL-6, a surrogate marker of pulmonary fibrosis), and anti-MDA5 Ab titers were elevated (ferritin 197.8 ng/mL, LDH 316 U/mL, KL-6 1271 U/mL, anti-MDA5 Ab > 150 index).