Localized relapse in bone marrow of extremities after allogeneic stem cell transplantation for acute lymphoblastic leukemia

We report a patient with a relapsed in bone marrow of extremities after allogeneic peripheral blood stem cell transplantation for acute lymphoblastic leukemia (ALL). The patient complained of pain in the right upper arm and left leg 15 months after transplantation. Magnetic resonance imaging (MRI) and fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) showed abnormal findings in bone marrow of upper and lower extremities. There were no findings of relapse in aspirates from the sternum and iliac bone marrow. Biopsy specimen from the iliac bone marrow showed normocellular marrow without leukemic cells. Biopsy specimen from the right humerus revealed marked leukemic cell infiltration in the bone marrow. This is apparently the first case of localized relapse of ALL in bone marrow of extremities. Physicians should be aware of unusual relapse sites of leukemia after allogeneic stem cell transplantation. MRI and FDG-PET may be of value in detecting this type of relapse.