Diagnostic pitfalls in pathological diagnosis of infectious disease: patients with syphilitic lymphadenitis often present with inconspicuous history of infection.

Retrospective study was applied to 16 cases of syphilitic lymphadenitis to elucidate the pathological diagnostic features. The typical morphology of syphilitic lymphadenitis includes: (i) well preserved or partially destroyed lymph node structure; (ii) reactive hyperplasia of lymph follicles with broadened germinal centers in the cortex and medulla of the lymph node; (iii) thickened fibrotic lymph node capsules with infiltration of plasma cells; and (iv) phlebitis and endarteritis in varying degree. Additional morphology includes: (i) focal histiocytes with ingested debris; (ii) noncaseating granuloma with epithelioid histiocytes and disperse giant cells; and (iii) hyperplastic centroblast and occasionally isolated mononuclear Reed-Sternberg cell-like giant cells. Treponema pallidum was identified in 15 of the 16 cases by immunohistochemical staining. The histopathological diagnosis of syphilitic lymphadenitis poses difficulty in differentiation from other infectious or neoplastic lymphadenopathies. The newly established Treponema pallidum antibody is sensitive to identification of Treponema pallidum in formalin fixed paraffin embedded tissue.