Tacrolimus-related posttransplant lymphoproliferative disorder presenting as autoimmune hemolytic anemia

Tacrolimus (formerly known as FK506) is a macrolide immunosuppressant that has been used to prevent rejection of solid organ allografts. Acute hemolytic anemia is one of the side effects associated with tacrolimus therapy, and two mechanisms have been described to account for acute hemolytic anemia in patients receiving tacrolimus: drug-induced hemolysis and alloimmune hemolysis resulting from donor lymphocytes derived from the allograft (passenger lymphocyte syndrome). We report a case of a liver transplant recipient who developed fatal autoimmune hemolytic anemia while under treatment with tacrolimus for allograft rejection, and in whom postmortem examination revealed a clinically unsuspected posttransplant lymphoproliferative disorder. This case implicates autoimmune hemolytic anemia as a novel mechanism of acute hemolysis in patients treated with tacrolimus and further suggests that acute hemolytic anemia in this group of patients may herald an occult lymphoproliferative disorder.