Posttransplant lymphoproliferative disorder: morphological picture and diagnostic difficulties.

Posttransplant lymphoproliferative disorder (PTLD) is a well-known complication of both solid organ and bone marrow transplantation. It includes a wide spectrum of proliferative changes ranging from reactive hyperplasia, borderline lesions to malignant lymphomas. PTLD develops in 1% to 10% of transplant recipients. We present 10 cases of PTLD. Five developed after renal, four after liver, and one after heart transplantation. Among the early lesions, we diagnosed two reactive plasmacytic hyperplasias; one infectious mononucleosis-like PTLD; one polymorphic lesion; and one "mixed" case of plasmacytic hyperplasia in one tonsil with a polymorphic PTLD in the second one. Among the lymphomas, we observed three diffuse large B-cell lymphoma (DLBCL); one mantle lymphoma; and one Hodgkin lymphoma-like PTLD. The morphological pictures of six PTLD cases were typical and posed no diagnostic problems. In the one case of plasmacytic hyperplasia, the lymph node morphology was atypical with atrophy of lymphoid components accompanying plasma cell proliferation. Contrary to a good prognosis of early, reactive PTLD, this patient experienced a rapid course and succumbed to sepsis. The most difficult case was a rare Hodgkin lymphoma-like PTLD, which was diagnosed only by a bone marrow biopsy. Because of its noncharacteristic immunophenotype, it was primarily diagnosed as an anaplastic lymphoma of the T-cell type. After additional immunohistochemical studies (BOB and OCT2), we established the final diagnosis of Hodgkin lymphoma-like PTLD. Due to the increasing number of organ transplantations, doctors of various specialties may encounter PTLD.