Steroid-Refractory Chronic Graft-Versus-Host Disease-Associated Isolated Myositis Successfully Treated With Ruxolitinib: A Case Report.

Chronic graft-versus-host disease (cGVHD) is a major late complication following allogeneic hematopoietic stem cell transplantation (HSCT), in which musculoskeletal involvement, particularly isolated myositis, is extremely rare. We report a case of cGVHD-associated myositis in a man in his 40s who underwent allogeneic bone marrow transplantation from a mismatched unrelated donor for Philadelphia chromosome-positive acute lymphoblastic leukemia. The patient developed acute GVHD, which was successfully managed with corticosteroid therapy. As GVHD did not recur, corticosteroids were gradually tapered and discontinued 1 year after transplantation. Forty-three days after discontinuation, the patient developed fever and progressive myalgia, leading to hospital admission. He presented with proximal muscle weakness and marked elevation of serum creatine kinase (CK). Infectious myositis and idiopathic inflammatory myopathies were carefully excluded. Muscle biopsy demonstrated inflammatory myopathy with infiltration of CD3-positive lymphocytes, a subset of which expressed programmed cell death protein 1 (PD-1), suggesting an immune-mediated process compatible with cGVHD-associated myositis. High-dose corticosteroid therapy resulted in partial clinical improvement; however, serum CK levels showed only transient reduction and failed to achieve sustained normalization, indicating an insufficient biochemical response. The addition of ruxolitinib was associated with subsequent normalization of CK levels and sustained clinical recovery, allowing for the successful tapering of corticosteroids. This case highlights a rare manifestation of cGVHD and suggests that ruxolitinib may represent an effective therapeutic option for steroid-refractory muscular involvement after allogeneic HSCT.