Abstract
In the present case report, a 3-year-old girl presented with a 1-week history of spontaneously resolving right knee pain. After 1 month, the patient had trouble ambulating due to painful swelling of their ankle. Rheumatic disease, specifically juvenile idiopathic arthritis, was considered. Blood examination could not be conducted because their blood sample was coagulated. T(1)-weighted magnetic resonance imaging (MRI) revealed abnormally low signals in the femur, tibia, fibula and foot bone marrow. Contrast-enhanced T(1)-weighted MRI revealed synovial contrast enhancement and synovial fluid retention in the right ankle joint. Blood analysis revealed a white blood cell count of 40,000/µl (blasts, 66%). In addition, a monoclonal increase in the number of lymphoblasts was observed. The patient was subsequently diagnosed with B-cell precursor acute lymphoblastic leukemia. Reports on leukemic arthritis resembling synovitis on MRI remain limited. The findings of this report indicated that pediatricians should consider leukemia in children presenting with joint symptoms.