A Rare Case of Primary Cutaneous Epstein-Barr Virus-Positive T Follicular Helper Cell Lymphoma.

We herein report a case of Epstein-Barr virus-positive primary cutaneous T follicular helper cell lymphoma (EBV-positive pcTFHL) in an elderly patient. The patient presented with multiple erythemas and cutaneous and subcutaneous nodules on the legs without internal organ involvement. Histology demonstrated diffuse infiltrates of atypical small- to medium-sized lymphoid cells in the dermis and subcutis associated with exocytosis in the epidermis and extensive necrosis in the deep dermis. Immunohistochemistry demonstrated that the atypical lymphoid cells were CD3- and CD4-positive T cells and expressed TFH cell markers. The CD4-positive atypical lymphoid cells were also diffusely positive for EBV byin situ hybridization, confirming the diagnosis of EBV-positive pcTFHL. The clinical course was progressive: large multiple cutaneous ulcers developed, and the patient died of fibrinous and organizing pneumonia due to COVID-19. The total clinical course was two years and two months after the onset of the skin rashes. This is the third case of EBV-positive pcTFHL that showed EBV infection exclusively in CD3- and CD4-positive T cells and had a lethal progressive clinical course.