Towards New Strategies: Case Report and Review of the Literature-Effective Use of JAK Inhibitor Baricitinib in a 4-Year-Old Boy with Anti-MDA5 Antibody-Positive Juvenile Dermatomyositis.

Juvenile dermatomyositis (JDM) is a rare, idiopathic autoimmune disorder characterized by inflammation of both muscle and skin, with a significant contribution from the interferon (IFN) pathway in its pathogenesis. Here, we present the case of a 4-year-old boy with JDM who tested positive for Mi2-α and MDA5 antibodies and showed combined muscle and skin involvement. In view of his markedly elevated IFN signature, the Janus kinase (JAK) inhibitor baricitinib was introduced very early as a targeted steroid-sparing agent in addition to standard immunosuppressive therapy. The patient experienced marked clinical improvement, with resolution of skin lesions, normalization of MDA5 antibodies, and a pronounced reduction in the IFN signature. This case highlights the potential efficacy of JAK inhibition in managing JDM with a high IFN signature and supports a mechanism-based, interferon-targeted treatment approach, in line with emerging evidence in refractory JDM. Further studies are warranted to define the role of JAK inhibitors in the treatment of JDM.