Bacterial lymphadenitis with the picture of a lymphoepithelioid cell lymphoma—Lennert's lymphoma

Abstract

Three cases with the typical light microscopic picture of lymphoepithelioid cell lymphoma (so-called Lennert's lymphoma) were investigated by electron microscopy. Surprisingly, Lennert's lymphoma could be excluded in two cases. These two cases exhibited, in addition to pleomorphic lymphocytes and epithelioid cells, macrophages with accumulations of bacteria, indicating that a bacterial infection was the cause of the disease. By comparing the typical case of Lennert's lymphoma with the other cases, we found several criteria for distinguishing between Lennert's lymphoma and bacterial lymphadenitis. In bacterial lymphadenitis: (1) small and medium-sized lymphocytes exhibited a wide cytological spectrum whereas the lymphocytes in Lennert's lymphoma were relatively uniform; the lymphocytes with prominent lysosome-like granules found in Lennert's lymphoma were not seen; (2) cytology and distribution of epithelioid cells were similar to those in Lennert's lymphoma; (3) epithelioid venules contained recirculating lymphocytes, which were rarely found in Lennert's lymphoma; (4) numerous interdigitating reticulum cells, fibroblasts and myofibroblasts were seen, but not in Lennert's lymphoma; (5) focal increase in reticulin fibres was the main difference in light microscopy; (6) rod-shaped bacteria were accumulated in the cytoplasm of a few macrophages. The presence of bacteria could not be demonstrated unequivocally by light microscopy. In both cases the large number of intracytoplasmic bacteria suggests that this unusual and until now unknown lymphadenitis is the result of an infection caused by facultative intracellular parasitic bacteria. The outcome of bacterial lymphadenitis that gives the false impression of Lennert's lymphoma is uncertain. Cure was achieved in one of our cases. The other patient died before therapy was commenced.

Revising the historical collection of epithelioid cell-rich lymphomas of the Kiel Lymph Node Registry: what is Lennert’s lymphoma nowadays?

“…Its rarity and the lack of firm diagnostic criteria partly explain why only a few reports on Lennert's lymphoma have been published so far. A morphological study of 402 epithelioid cell-rich lymphomas of the Kiel Lymph Node Registry was performed by Patsouris et al, [4][5][6][7][8][9] and Lennert's lymphoma and its differential diagnosis were further characterized by pure morphology. We have now applied immunohistochemistry to epithelioid cell-rich lymphomas that are still available at the Kiel Lymph Node Registry.…”

Systemic Mycobacterium kansasii infection mimicking peripheral T‐cell lymphoma

“…Two cases of bacterial lymphadenitis with features of Lennert's lymphoma were reported in 1989 (19). Here we add two cases of M. kansasii infection with poorly formed granulomas mimicking peripheral T‐cell lymphoma.…”

“…From a literature review we found that the epithelioid histiocytes in Lennert's lymphoma tend to be distributed regularly and uniformly, and aggregate in small clusters (fewer than 10 cells per cluster). In contrast, infectious granulomas are usually well formed, enclosed within a fibroblastic rim, irregularly distributed, and in larger clusters (more than 10 cells per cluster) (17–19, 32). Also helpful are neutrophilic aggregates in the latter, as well as ancillary studies, e.g., acid‐fast stains and TCR gene rearrangement.…”

“…The above features are usually different from those in malignant lymphomas and therefore the morphologic criteria for differentiation of infectious granulomas and Lennert lymphoma have not been described in detail in the literature (4, 5, 9). Two cases of bacterial lymphadenitis with features resembling Lennert lymphoma have been reported but the nature of the bacteria was not identified (19). Herein, we report two cases of systemic NTM infection whose features closely resembled those of peripheral T‐cell lymphoma morphologically and clinically.…”