Isolated Positive Treponemal Test in Pregnancy and Placental Abnormalities Without Confirmed Syphilis Infection: A Case Report

Abstract

Syphilis screening during pregnancy is essential to prevent congenital syphilis, yet diagnostic challenges arise when clinical presentation, serologic results, and pathologic examination are discordant. We report the case of a 39-year-old pregnant patient with a reactive enzyme immunoassay (EIA) at delivery, despite prior nonreactive syphilis serologies and a negative confirmatory test postpartum. Placental examination revealed multiple intervillous abscesses and chronic villitis, raising concern for congenital syphilis. However, immunohistochemistry (IHC) for Treponema pallidum yielded conflicting results across laboratories. Despite the lack of confirmed maternal infection, the neonate underwent a full congenital syphilis evaluation and received penicillin treatment. This case highlights the complexities of interpreting isolated positive treponemal tests, the limitations of placental pathology in syphilis diagnosis, and the need for standardized management algorithms to prevent misclassification, overtreatment, and undue emotional and healthcare burden. Interdisciplinary communication and rapid confirmatory testing are critical to optimizing maternal and neonatal outcomes.

Keywords: congenital syphilis; false-positive treponemal test; placental pathology; pregnancy; syphilis screening.

Figure 1

A cut section through the placenta with the fetal surface at the top and the maternal surface at the bottom of the image. Multiple yellow-white nodules are scattered throughout the dark red villous parenchyma.

Figure 2

A microscopic section of one of the placental lesions shows central abscess formation with neutrophilic debris and necrotic villi (star), rimmed by villi showing chronic inflammation (chronic villitis) (arrows). Hematoxylin and eosin stain, 10x.