Kikuchi disease with an exuberant proliferation of large T-cells: a study of 25 cases that can mimic T-Cell lymphoma.

Exuberant large T-cell proliferations in Kikuchi disease can potentially be misdiagnosed as lymphoma. In this study, we explore their clinicopathological features and summarize key points that can be used to distinguish them from T-cell lymphoma. The cohort consisted of 25 cases of Kikuchi disease with an exuberant large T-cell proliferation, which, in part, mimicked lymphoma. The median age was 25 years with a female:male ratio of 4:1. By B-scan ultrasonography, patients presented with either isolated lymphadenopathy (68%) involving the cervical and axillary regions or generalized lymphadenopathy (32%). Histologically, lymph nodes showed paracortical and interfollicular expansion by sheets of large cells associated with karyorrhectic debris. Histiocytes and plasmacytoid dendritic cells were present in the background. No case showed complete effacement of lymph node architecture. The large cells were CD8-positive cytotoxic T-cells with a high proliferation rate. These T-cells showed decreased BCL-2 in 17 (68%) cases. CD5 expression was decreased in 10 (40%) cases. Histiocytes in the background were positive for myeloperoxidase. Clonal TRG and/or TRB rearrangements were detected in 2 of 10 (20%) cases. In conclusion, large T-cell proliferations in Kikuchi disease can be alarming at the morphologic and immunophenotypic levels and need to be distinguished from T-cell lymphoma. Clinical features helpful in the differential diagnosis include young patients and lymphadenopathy involving the cervical and axillary regions. Major pathologic features helpful in this differential diagnosis include partial involvement of the lymph node and the presence of karyorrhectic debris, crescent-shaped histiocytes, and/or loose aggregates of plasmacytoid dendritic cells.