P049 A well-behaved ulcer: Epstein–Barr virus-positive mucocutaneous ulcer mimicking lymphoma in an immunosuppressed dermatology patient

Abstract

A 66-year-old woman had long-standing severe atopic eczema requiring multiple immunosuppressants, most recently upadacitinib, as well as multiple squamous cell carcinomata. She presented with a painless ulcer on the left oral commissure. Examination revealed a well-circumscribed, circular, shallow ulcer with no associated lymphadenopathy or organomegaly. Punch biopsy demonstrated a dense lymphocytic infiltrate with dark polymorphic (but not overtly anaplastic) morphology. No Hodgkin or Reed–Sternberg-type cells were detected. The main population of atypical lymphocytes expressed EBERs and Epstein–Barr virus (EBV) latent membrane protein. Immunohistochemistry showed CD30+, CD15−, ALK1−, fascin±, CD25±, CD20+, CD79a±, PAX5±, OCT2+, CD3−, CD2−, CD5−, CD4−, CD8−, CD10−, BCL6±, MUM1+, Ki67high. Neutrophil granulocytes and histiocytoid cells were scant, and plasma cells and eosinophils were absent. EBV and B-cell markers were neatly colocalized. Histological findings showed an EBV-positive mature B-cell neoplasm. Differential diagnoses included EBV-positive mucocutaneous ulcer (EBV-MCU) and EBV-positive diffuse large B-cell lymphoma (EBV-DLBCL), which cannot be differentiated on histology, immunophenotyping, clonality or next-generation sequencing. Clinically, a multidisciplinary approach was taken. Positron emission tomography–computed tomography showed no evidence of systemic lymphoma. Serum lymphocyte subsets demonstrated global reduction in B- and T-lymphocyte populations, with preserved immunoglobulin levels and no paraprotein or light-chain abnormality. Given the localized presentation, absence of systemic disease and subsequent spontaneous resolution of the ulcer, EBV-MCU was favoured. EBV-MCU is a distinct EBV-driven lymphoproliferative disorder first recognized by the World Health Organization in 2017. It presents as a solitary, sharply circumscribed mucocutaneous ulcer, commonly oropharyngeal, and often in the context of immunosuppression. Histologically, it closely mimics EBV-DLBCL; however, its clinical course is indolent, often spontaneously regressing. This case highlights EBV-MCU as a diagnostic entity in the context of Janus kinase 1 inhibition and cumulative prior immunosuppression for eczema. This also underscores the importance of clinical suspicion for EBV-associated lymphoproliferative disorders in this cohort, as well as clinicopathological correlation and appropriate staging to avoid overtreatment.