Inflammatory pseudotumor of lymph nodes (IPT-LN) represents all unusual cause of lymphadenitis oh unknown etiology. Upon the observation of a case of IPT-LN associated with Treponema pallidum (Tp) infection, we analyzed a series of 9 IPT-LN and 9 extranodal IPT (spleen, 4 cases: lung, orbit, gut, skin, and liver) tar the presence of Tp, using a polyclonal antibody anti-Tp. At the time of biopsy, none of the patients was, suspected for lactic infection, nor specific serologic tests were available. IPT-LN areas extensively involved the nodal parenchyma in 4 cases, whereas they were focal in the remaining S cases. Capsular thickening and inflammation (6/9), venulitis (3/9), small granalomas (3/9), and follicular hyperplasia (7/9) were observed in the associated lymphoid parenchyma. Tp were detected in 4/9 cases of LN-IPT and in none of the extranodal IPT. Tp were extremely abundant within the IF F areas and in the perivascular tissues in the surrounding parenchyma, whereas they were scattered within the capsule. In Tp+ cases, marked follicular hyperplasia was the single distinctively associated feature. Double immunostains revealed that Tp were predominantly contained in the cytoplasm of CD11c+ CD163+ macrophages, sonic of which co-expressed HLA-DR. In addition, scattered S100+ interdigitating dendritic cells also showed intracytoplasmic Tp. This study shows that a significant number of IPT-LN is associated with Tp infection. A spirochetal etiology c:in he suspected in cases of IPT-LN. independently from the extension of the lesions, especially when pronounced follicular hyperplasia is found. Infection by Tp of macrophages and dendritic cell, are in keeping with ill vitro data and indicate that immune mediated mechanisms may he involved ill the pathogenesis of the lesions.
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