Advances in Juvenile Dermatomyositis: Pathophysiology, Diagnosis, Treatment and Interstitial Lung Diseases—A Narrative Review

Juvenile idiopathic inflammatory myopathy (JIIM) is a rare systemic autoimmune disease characterized by skeletal muscle weakness with or without a skin rash. Juvenile dermatomyositis (JDM) is the most common subtype of JIIM, accounting for 80% of JIIM. Recent studies identified several myositis-specific autoantibodies (MSAs) and myositis-associated autoantibodies (MAAs). Each MSA or MAA is associated with distinct clinical features and outcomes, although there are several differences in the prevalence of MSA/MAA and autoantibody-phenotype relationships between age and ethnic groups. Histopathological studies have revealed critical roles of type I interferons and vasculopathy in the development of JDM. Serological classification mostly corresponds to clinicopathological classification. Novel therapeutic agents, such as biologics and Janus kinase inhibitors (JAKi), have been developed; however, to date, there is a lack of high-level evidence. As advances in treatment have reduced the mortality rate of JIIM, recent studies have focused on medium- and long-term outcomes. However, rapidly progressive interstitial lung disease (RP-ILD) remains a major cause of death in anti-melanoma differentiation gene 5 autoantibody-positive JDM. Early diagnosis and intervention using a multi-drug regimen is critical for the treatment of RP-ILD. Rituximab and JAKi may reduce mortality in patients with JDM-associated RP-ILD refractory to conventional therapy.