Sequential Sinusoidal Obstruction Syndrome and TA-TMA After Haploidentical Hematopoietic Stem Cell Transplantation: Diagnostic and Therapeutic Challenges

Background/Objectives: Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) has expanded donor availability for patients with acute myeloid leukemia; however, it is associated with a high risk of endothelial complications. Among them, sinusoidal obstruction syndrome (SOS) and transplant-associated thrombotic microangiopathy (TA-TMA) are life-threatening conditions with overlapping clinical features, making early diagnosis and management challenging. Case Presentation: We report the case of a 47-year-old woman with acute myeloid leukemia who underwent haploidentical HSCT and developed sequential endothelial complications. On day +11 post-transplant, she presented with weight gain (>5%), hyperbilirubinemia (44 μmol/L), elevated liver enzymes (ALT 2228 U/L and AST 3477 U/L), and multi-organ dysfunction, consistent with probable SOS according to EBMT criteria. Intensive supportive care, glucocorticosteroids, and hemodiafiltration resulted in partial clinical improvement. Subsequently, on day +22, the patient developed progressive thrombocytopenia, hemolytic anemia (hemoglobin 71 g/L), elevated lactate dehydrogenase (3129 U/L), undetectable haptoglobin, and schistocytosis (up to 3.9%), accompanied by neurological symptoms, leading to the diagnosis of TA-TMA. Results: Management included discontinuation of tacrolimus, initiation of plasma exchange, and complement inhibition with eculizumab, along with ruxolitinib for graft-versus-host disease prophylaxis. This approach resulted in rapid clinical and laboratory improvement, including resolution of hemolysis, reduction in schistocytes (to 1%), normalization of lactate dehydrogenase, and regression of neurological symptoms. The patient was discharged in stable condition, although requiring ongoing renal replacement therapy. Conclusions: This case highlights the complexity of diagnosing and managing sequential endothelial complications after haplo-HSCT. SOS and TA-TMA may reflect overlapping manifestations of endothelial injury rather than entirely isolated complications.