Primary cutaneous B-cell posttransplant lymphoproliferative disorders mimicking pyoderma gangrenosum in a renal transplant recipient.

Posttransplant lymphoproliferative disorder is an uncommon complication of immunosuppression following solid organ or hematopoietic stem cell transplants. Primary cutaneous posttransplant lymphoproliferative disorder with isolated skin involvement but without systemic involvement is rare. We report a 50-year-old woman, a renal transplant recipient on long-term immunosuppression, who presented with a rapidly expanding ulcer on her right posterior thigh after a skin incision. Although the clinical presentation was similar to that of pyoderma gangrenosum, pathological investigation confirmed Epstein-Barr virus-associated primary cutaneous B-cell posttransplant lymphoproliferative disorder. Initially, we reduced her immunosuppression. As the ulcer rapidly expanded, we initiated R-CHOP chemotherapy, consisting of rituximab, cyclophosphamide, doxorubicin, and prednisolone. Owing to the complications from cytomegalovirus retinitis, we were only able to administer two courses of chemotherapy. However, after continuous administration of ganciclovir, the skin ulcer regressed and completely healed, leaving a scar five months after her first visit. Since pyoderma gangrenosum is a diagnosis of exclusion, ulcerative skin lesions, similar to the clinical presentation of pyoderma gangrenosum, should be subjected to pathological investigation for accurate diagnosis.