Methods: This retrospective cross-sectional study included 26 patients with anti-MDA5+ DM and 43 patients with anti-MDA5 negative (anti-MDA5–) idiopathic inflammatory myopathy (IIM) who were examined by 18F-FDG PET/CT from January 1, 2017 to December 31, 2020. The gene discussed is IFIH1; the disease is dermatomyositis.