Signet-ring histiocytes in typhoid fever

Jianfeng Zhu and Wei Guo

A 41-year-old man presented to our institution with a 2-week history of fever, diarrhea, and anorexia after a trip to Bangladesh. Physical examination revealed no jaundice, lymphadenopathy, or organomegaly. His blood cell counts were within normal range except for eosinopenia (0%) and thrombocytopenia (50 × 109/L). Wright-Giemsa–stained bone marrow showed histiocytes (panel A; original magnification ×400) with foamy cytoplasm and eccentric nuclei (panel B; original magnification ×1000), some resembling signet-ring cells (panel C; original magnification ×1000) and engulfing erythroblasts (panel D; original magnification ×1000). Tropical diseases such as malaria and dengue fever were excluded. Bone marrow culture was positive for Salmonella typhi. Historically, these histiocytes were referred to as “typhoidal cells” and were first reported in 1975 [Lancet. 1975;ii(7941):927-928].

S typhi resides in macrophages during the course of typhoid infection, and the association between typhoid fever and signet-ring histiocytes found in bone marrow has been sporadically described in the literature. These signet-ring histiocytes could be identified in bone marrow smears in as many as half of the cases. Therefore, signet-ring histiocytes could serve as a morphological indicator for the differential diagnosis of typhoid fever, especially among those reporting a recent trip to endemic areas.


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