(421) Histopathologic changes associated with Treponema pallidum detection in placental tissues

Characterize histopathologic changes in syphilis-exposed placentas with and without immunohistochemical (IHC) detection of Treponema pallidum in placental tissues.

Study Design:
This is a retrospective cohort study of patients delivered after syphilis diagnosis at a large public hospital. Among placentas for which placental pathologic evaluation was available and IHC stain on umbilical cord or placental tissues was performed for detection of T. pallidum, we compared maternal syphilis characteristics and histopathologic changes among IHC+ and IHC- placentas.

Results:
From January 1, 2010, through June 30, 2025, 126 placentas from gravidas with syphilis in pregnancy had IHC stain, including 22 IHC(+) and 104 IHC(-). Early syphilis, higher maternal RPR, later EGA at diagnosis, lack of benzathine penicillin G (BPG) exposure before delivery, and stillbirth were more common among IHC+ placentas. Congenital syphilis was diagnosed among 100% of IHC+ and 18(18%) of IHC- groups. Among gravidas treated prenatally, interval (d) to delivery was shorter (6 [3-17] vs 136[66-180], p< 0.001] with odds of IHC+ decreased by 97% if the BPG-delivery interval was more than 17 days. IHC positivity was associated with LGA placentas, acute maternal and fetal inflammatory responses, and specific villous changes including increased histiocytic villitis with Hofbauer cells and increased fetal RBCs. Maternal vascular lesions suggestive of malperfusion were not different. Among fetal villous or vascular lesions, villous karyorrhexis and vascular occlusion or involution in chorionic plate vessels were more common in IHC+ placentas.

Conclusion:

Immunohistochemical staining for Treponema pallidum assists with characterization of congenital syphilis-associated placental histopathologic changes. Earlier diagnosis and treatment of gravidas with syphilis decreases the acute maternal and fetal inflammatory response in the placenta linked to prematurity, fetal distress and stillbirth.