Cutaneous Epstein-Barr Virus (EBV) Positive Diffuse Large B-Cell Lymphoma (DLBCL) Arising in Dermatomyositis Treated With Mycophenolate Mofetil

Dermatomyositis (DM) is an autoimmune inflammatory myopathy characterized by hallmark cutaneous findings and proximal muscle weakness, often requiring systemic immunosuppressive therapy for disease control. Mycophenolate mofetil (MMF) is increasingly utilized due to its favorable safety profile; however, prolonged immunosuppression may predispose patients to lymphoproliferative disorders (LPDs), including rare Epstein-Barr virus (EBV)-associated diffuse large B-cell lymphoma (DLBCL). We present a 73-year-old woman with biopsy-proven DM who developed an EBV-positive cutaneous DLBCL of the scalp while receiving MMF therapy. She initially presented with a two-year history of a widespread, symptomatic rash and proximal muscle weakness, with clinical and serologic findings supporting DM. Following treatment with corticosteroids and MMF, her disease improved; however, four months later, she developed a new erythematous crusted scalp plaque. Histopathologic evaluation demonstrated an ulcerated dermal infiltrate of atypical lymphoid cells with high proliferative index and immunophenotypic features consistent with EBV-positive DLBCL. Systemic evaluation with PET/CT was negative for extracutaneous disease. MMF was discontinued, and she was treated with rituximab, resulting in complete resolution of both lymphoma and dermatomyositis. This case highlights a rare presentation of immunodeficiency-associated LPD manifesting as an isolated cutaneous lesion on the scalp in a patient with autoimmune disease on immunosuppressive therapy. It underscores the importance of maintaining a high index of suspicion for malignancy in DM patients, particularly those receiving MMF. Regular skin examinations and prompt biopsy of new or atypical lesions are critical for early detection. Rituximab represents an effective therapeutic strategy addressing both underlying autoimmune disease and EBV-associated lymphoproliferation.