Hepatic veno-occlusive disease complicated with extreme hyperammonaemia (920 µmol/L) treated with defibrotide, lactulose, rifampin and haemodialysis.

Hepatic veno-occlusive disease (VOD)/sinusoidal obstructive syndrome (SOS) is a severe complication that can occur following haematopoietic stem cell transplant (HSCT) with high-intensity conditioning chemotherapy regimens. Severe VOD/SOS, often characterised by multiorgan failure, is associated with a high mortality rate. This case report details the complex clinical course of a male patient in his mid-20s, recently diagnosed with B cell acute lymphoblastic leukaemia, who underwent allogeneic HSCT. Based on the 2023 European Society for Blood and Marrow Transplantation (EBMT) criteria, the patient developed very severe VOD/SOS, prompting immediate treatment with defibrotide. Unexpectedly, he developed profound hyperammonaemia exceeding 900 µmol/L, leading to encephalopathy and cerebral oedema. Despite aggressive interventions including defibrotide, lactulose, rifampin and haemodialysis, the patient passed away due to cerebral oedema and pulseless electrical activity arrest. We theorise the hyperammonaemia is disproportionate to his hepatic dysfunction and is possibly secondary to an acquired defect of the urea synthesis consistent with idiopathic hyperammonaemia, a rare complication in patients receiving intense conditioning chemotherapy.