Sinusoidal Obstruction Syndrome Post-allogeneic Transplantation: A Complex Multisystem Challenge.

We present the case of a 41-year-old female with chronic myeloid leukemia (CML) in blast crisis who underwent haploidentical allogeneic stem cell transplantation. Her post-transplant course was complicated by neutropenic sepsis and mucositis, followed by the development of sinusoidal obstruction syndrome (SOS) on post-transplant day (POD) 10, evidenced by rising hyperbilirubinemia (peak 22.2 mg/dL) and significant weight gain primarily due to fluid retention. Imaging confirmed hepatosplenomegaly and portal vein dilation, leading to the SOS diagnosis. Defibrotide was initiated on POD 16, leading to a progressive decline in bilirubin levels (from 22.2 mg/dL to 2.4 mg/dL by POD 22), suggesting a therapeutic response. However, thrombocytopenia and gastrointestinal hemorrhage necessitated dose interruptions. Supportive care included fluid management, albumin infusions, and diuresis, but hepatorenal syndrome developed, requiring continuous renal replacement therapy (CRRT). On POD 27, she developed acute hypoxic respiratory failure, requiring a high-flow nasal cannula and later vasopressor support for worsening hemodynamic instability. Despite intensified critical care measures, including broad-spectrum antimicrobials and transfusion support, her condition deteriorated, leading to progressive multiorgan failure and transition to comfort care on POD 34. This case highlights the diagnostic and therapeutic challenges of severe post-transplant SOS, emphasizing the need for early intervention, a tailored risk-benefit assessment of defibrotide, and multidisciplinary critical care strategies for high-risk patients.