Extramedullary plasmacytoma exclusively localized in transplanted kidney: Post-transplant lymphoproliferative disorder or monoclonal gammopathy of renal significance?

Post-Transplant Lymphoproliferative Disease (PTLD) is defined as a malignancy that occurs post solid organ transplant (SOT). The incidence of PTLD in kidney transplant is lowest amongst all SOT with a majority having a monomorphic pattern that is commonly B cell driven. Plasmacytic variants of PTLD have been rarely reported, with only a handful of cases being clonal in nature. Here we report a unique case of a plasmacytoma-like PTLD with IgG-K restriction confined entirely to the kidney allograft, without evidence of any clonal plasma cell in the bone marrow or other extramedullary site. This case highlights an extremely rare disease, describes a diagnostic dilemma, reports the unconventional management, and poses more interesting questions about the pathophysiology of this disease.