A Case of Refractory Polyarticular Juvenile Idiopathic Arthritis Post-hematopoietic Stem Cell Transplantation Successfully Treated With Ruxolitinib.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) may trigger secondary autoimmune diseases, with autoimmune arthritis representing a rare yet challenging complication. Here, we report a six-year-old male who developed polyarticular juvenile idiopathic arthritis (JIA) three years after allo-HSCT for lymphoma. Despite resistance to multiple biologic disease-modifying anti-rheumatic drugs (bDMARDs), including adalimumab and tocilizumab, treatment with the Janus kinase 1/2 inhibitor ruxolitinib achieved clinical remission sustained for over two years without significant adverse events or lymphoma relapse. Ruxolitinib may represent a viable therapeutic option for refractory secondary JIA post-allo-HSCT, particularly when conventional bDMARDs fail.