Methotrexate-induced primary cutaneous diffuse large B-cell lymphoma with an 'angiocentric' histological morphology.

A patient with a 25-year history of rheumatoid arthritis and a 3-year history of methotrexate treatment developed a generalized papular rash. The papules rapidly became necrotic and then resolved, leaving a depressed scar. The rapid course of lesion development and regression was reminiscent of pityriasis lichenoides. Histology revealed a nodular infiltrate composed of a mixture of pleomorphic large B cells positive for CD20, CD30 and CD79a, and of small T cells positive for CD3 and CD4. The T cells had a striking angiocentric distribution, with some of the vessels exhibiting fibrinoid necrosis of the vessel wall reminiscent of lymphomatoid granulomatosis. However, B cells were consistently negative for Epstein-Barr virus (EBV) antigen expression. A thorough examination excluded involvement of organs other than the skin. Thus, this patient was classified as having a rare form of an EBV-negative primary cutaneous T-cell-rich B-cell lymphoma in association with methotrexate treatment.