Post-Transplant Lymphoproliferative Disorder Manifesting as Lymphoplasmacytic Lymphoma Accompanying With Hemophagocytic Lymphohistiocytosis.

Post-transplant lymphoproliferative disorder (PTLD) is a potentially life-threatening complication, often associated with Epstein-Barr virus (EBV) in the early period after hematopoietic stem cell transplantation (HSCT). Clinical manifestations range from localized to disseminated disease. The cornerstone of therapy is the reduction of immunosuppression and/or immunochemotherapy. We report a 39-year-old female who developed PTLD presenting as lymphoplasmacytic lymphoma (LPL) associated with hemophagocytic lymphohistiocytosis (HLH). Diagnostic evaluation was blurred by features of severe hepatic acute graft-versus-host disease (GVHD). An initial treatment consisted of high-dose steroids, but it failed. As second-line treatment, ruxolitinib and mycophenolate mofetil were administered, but they were ineffective, and the patient's condition worsened. Further detailed evaluation revealed the presence of monoclonal protein immunoglobulin G (IgG) lambda and bone marrow infiltration by clonal plasmacytoid B lymphocytes. The HLH criteria were also met. Immunosuppression was discontinued, and dexamethasone with rituximab was initiated, but no response was observed. The patient eventually died from multiple organ failure. The learning points from this case emphasize that HLH in the context of PTLD remains underreported, with few cases documented in the literature. Studies indicate that EBV plays a central role in pathogenesis, often presenting with systemic inflammation and immune dysregulation. Diagnostic challenges arise due to overlapping clinical features with other post-transplant complications. Treatment strategies vary but often involve balancing immunosuppression reduction and chemotherapy, with rituximab being a cornerstone for EBV-driven cases. This case underscores the necessity of early recognition to mitigate severe outcomes.