Paroxysmal Nocturnal Hemoglobinuria-Driven Hepatic Vein Thrombosis: A Case of Budd-Chiari Syndrome in Disguise.

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired hematopoietic stem cell disorder characterized by complement-mediated intravascular hemolysis and a markedly increased risk of thrombosis, including at atypical splanchnic sites. We report a 26-year-old woman who presented with progressive abdominal distension, right upper quadrant pain, early satiety, and morning dark-colored urine. Investigations revealed normocytic anemia, biochemical evidence of intravascular hemolysis, moderate ascites, hepatomegaly, and elevated D-dimer; direct and indirect antiglobulin tests were negative. Flow cytometry using FLAER (Fluorescent AERolysin) and CD55/CD59 confirmed large PNH clones in granulocytes and monocytes, consistent with classic PNH complicated by hepatic vein thrombosis, Budd-Chiari syndrome (BCS). She received therapeutic anticoagulation and complement inhibition with eculizumab, alongside supportive transfusions and monitoring, with progressive clinical and laboratory improvement. This case emphasizes that BCS may be the presenting manifestation of PNH in young patients without conventional thrombotic risk factors and highlights the importance of prompt flow cytometry testing and initiation of complement inhibition to reduce morbidity and recurrence of thrombotic events.