Polymyositis in a child with thalassemia after hematopoietic stem cell transplantation: A case report.

RATIONALE: Polymyositis (PM) is a rare neuromuscular phenotype of chronic graft-versus-host disease (cGVHD). Although glucocorticoids have been shown to be effective in the treatment of PM, most people experience poor treatment response and poor prognosis.

PATIENT CONCERNS: A six-year-old boy with thalassemia received allogeneic hematopoietic stem cell transplantation (HSCT) and consequently developed sudden myasthenia of limbs 17 months after the transplant.

DIAGNOSES: Medical history, current symptoms, laboratory examinations, and imaging findings of the patient indicated cGVHD complicated with PM.

INTERVENTIONS: He was then given high-dose corticosteroid therapy, including tacrolimus, ruxolitinib, and rituximab.

OUTCOMES: Twenty-three months after transplantation, creatine kinase levels returned to normal range, and the MRI showed that the original muscle edema signal was significantly improved. The patient's muscle weakness continued to improve, and his overall condition was good.

LESSONS: This report suggests that glucocorticoids combined with immunosuppressants may be effective against polymyositis. Rituximab and ruxolitinib may be a good choice in treating polymyositis.