Identification of anti-thrombopoietin receptor antibody in prolonged thrombocytopenia after allogeneic hematopoietic stem cell transplantation treated successfully with eltrombopag.

A 55-year-old female with stage IVA follicular lymphoma in third complete remission underwent allogeneic peripheral blood stem cell transplantation. Neutrophil engraftment was achieved on day +18; however, platelet counts remained below 10 × 10(3)/µL, necessitating transfusions twice a week for more than 3 months. Bone marrow showed a decreased number of megakaryocytes with hypolobulated nuclei. No graft versus host disease, viral infection, or disease relapse was observed. Furthermore, severe thrombocytopenia below 5.0 × 10(3)/µL refractory to transfusion appeared on day +240 after influenza virus infection. Treatments with intravenous immunoglobulin, romiplostim, and rituximab were administered without any recovery. Subsequently, eltrombopag was initiated on day +443, after which platelet counts rose gradually and continued to rise above 20 × 10(3)/µL after 10 weeks of administration. The serum thrombopoietin (TPO) level was markedly elevated, and anti-TPO receptor (TPOR) antibody was detected in the patient's serum. Anti-TPOR antibody may play an important role in some cases of prolonged thrombocytopenia after allogeneic hematopoietic stem cell transplantation with unknown etiology, and eltrombopag could be a novel therapeutic option for such cases.