Angioimmunoblastic T-Cell Lymphoma with Polyclonal Proliferation of Plasma Cells: A Cautionary Note for Flow Cytometry Interpretations

Angioimmunoblastic T-cell lymphoma (AITL) is a lymphoproliferative disorder of mature T follicular helper cells. Atypical lymphoid cells were observed in the bone marrow of an 80-year-old woman, and the flow cytometric determined immunophenotypes of B-cells were unusual, that is, CD19+, CD20-, and CD22- with lambda light chain restriction. Initially, we suspected BM involvement of B-cell lymphoma based on the presence of abnormal B-cells. However, the patient was diagnosed with AITL involving BM. A re-analysis of flow cytometric immunophenotyping revealed a minor, aberrant T-cell population, and the lambda light chain restriction observed by surface staining was considered non-specific binding. This case demonstrates B-cells in patients with EBV-positive T-cell lymphoma may exhibit immunophenotypes resembling those of plasma cells, and that proliferation of abnormal B-cells or plasma cells could also potentially mask underlying T-cell lymphoma. A more integrated approach is required for accurate diagnosis.