Primary Cutaneous Monomorphic Post-transplant Lymphoproliferative Disorder Mimicking Squamous Cell Carcinoma In Situ.

Post-transplant lymphoproliferative disorder (PTLD) is a term used to describe a range of lymphoproliferative disorders that occur after solid organ transplant. Although the clinical presentation is variable, primary cutaneous PTLD typically presents as isolated nodules that appear as dermal-based proliferations. We present a case of a 70-year-old woman with a history of a kidney transplant who presented with a 2-month history of an asymptomatic, erythematous plaque on the right shin, clinically suspected to be squamous cell carcinoma in situ. Histomorphology demonstrated a dermal proliferation of atypical plasma cells with dense chromatin, variable nucleoli, and irregular nuclear borders. The atypical plasma cells were positive for Epstein-Barr virus by in situ hybridization and markedly kappa-restricted by RNAscope in situ hybridization. A diagnosis of cutaneous monomorphic PTLD, plasma cell neoplasm variant, was rendered, a rare diagnosis in the skin. Treatment for PTLD typically involves reduction of immunosuppression, although our patient progressed and developed new lesions despite this intervention. In this study, we present an atypical presentation of cutaneous PTLD, plasma cell neoplasm variant, presenting as squamous cell carcinoma in situ.