Splenic Irradiation Preceding Allogeneic Hematopoietic Stem Cell Transplantation As a Possible Risk Factor of Sinusoidal Obstruction Syndrome: A Report of Three Cases

Introduction: Splenomegaly is frequently encountered in patients with myeloproliferative neoplasms. Splenomegaly is associated with an increased incidence of engraftment failure during allogeneic hematopoietic stem cell transplantation (allo-HSCT), and some centers perform prior low-dose splenic irradiation (LDSI) which has been reported to be both safe and effective. However, we report conflicting results by presenting three allo-HSCT patients undergoing LDSI that subsequently developed sinusoidal obstruction syndrome (SOS). Case Presentation: The underlying diseases of the presented cases were atypical chronic myeloid leukemia, secondary myelofibrosis following essential thrombocythemia, and acute myeloid leukemia transforming from myeloproliferative neoplasm, unclassifiable. Endothelial Activation and Stress Index (EASIX) scores of the 3 patients were 0.40, 3.82, and 4.40, respectively. Conclusion: SOS is a potentially fatal complication of allo-HSCT, and the mortality rates of severe cases are reported to be above 80%. LDSI has not been recognized as a risk factor of SOS to date. Alternative management methods of splenomegaly during allo-HSCT such as ruxolitinib administration may be safer compared to LDSI.