An Unforeseen Diagnosis After Liver Transplantation for Acute Liver Failure: Extranodal NK/T-Cell Lymphoma.

Acute liver failure (ALF) is a medical emergency characterized by hepatic encephalopathy in patients with recent-onset jaundice and coagulopathy. We present a case of a patient who developed ALF secondary to NK/T-cell lymphoma, with the diagnosis confirmed via histopathological analysis of the explanted after liver transplantation. A 50-year-old woman with no significant medical history was transferred to our institution with severe acute liver injury. On admission, she exhibited drowsiness, jaundice, and hepatosplenomegaly. The patient denied alcohol use but reported consuming horsetail tea (Equisetum spp). We hypothesized drug-induced liver injury as the main diagnosis, attributing to the use of horsetail tea. Despite intensive supportive care, her condition continued to deteriorate, prompting urgent deceased-donor liver transplantation. Histopathological analysis of the explant revealed hepatic parenchyma infiltration by atypical lymphoid cells positive for CD2, CD3, CD8, CD56, and CD38, with Ki-67 > 95% and positive EBV in situ hybridization. The graft biopsy and appendix showed identical findings, confirming a high-grade Stage IV extranodal NK/T-cell lymphoma (ENKTL). Given her critical condition, a modified chemotherapy regimen was initiated. Subsequent complications included severe chemotherapy-induced pancytopenia, febrile neutropenia, invasive aspergillosis, and multiorgan failure, culminating in death 33 days post-transplant. This case highlights the diagnostic challenges of rare non-Hodgkin lymphoma with extranodal presentations. Although horsetail tea is associated with liver injury, its contribution to ALF remains insufficiently defined, reinforcing the importance of excluding alternative causes. ENKTL and other malignancies should be considered in indeterminate ALF, even without imaging findings, atypical lymphocytes in peripheral blood/ascites, or overt clinical suspicion of malignancy.