Diagnostic Approach to Syphilis – Not So Painless After All

October 17, 2024

Written by Nickolas Srica

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There continues to be a lack of evidence to strongly recommend one treponemal assay over another in the diagnosis of syphilis, particularly given the varying accuracy of each test depending on the stage of the disease. For now, this review suggests the diagnostic algorithm recommended by the CDC (see below!) seems to be a reasonable approach, but more trials are needed to refine this.

Diagnosing syphilis, not quite as painless as that chancre…
Syphilis, a sexually transmitted infection caused by the spirochete Treponema pallidum, can present in various different stages, ranging from the painless chancre of primary syphilis to the potentially devastating multi-system involvement of tertiary syphilis. Diagnosis classically involves starting with a “non-treponemal” test such as rapid plasma reagin (RPR), then confirming with a “treponemal test” like the T. pallidum particle agglutination (TP-PA). Recently, a shift toward treponemal immunoassays for initial screening has occurred, but what exactly does the evidence say about these tests and their accuracy, and which should we be ordering?

This was a review of the current evidence, which included two systematic reviews, regarding the accuracy of the tests available for the diagnosis of syphilis and their operating characteristics. Most notably, the authors point out the paucity of high-quality data from many of these original trials, largely due to a number of limitations including their retrospective designs, the unclear clinical staging of patients in these trials, incomplete data inclusion, small overall sample sizes, small number with children enrolled, and differences in reference standards – just to name a few.

How will this change my practice?
Based on this review of the current evidence, these authors conclude that, for now, the diagnostic algorithm recommended by the CDC seems to be the best approach (check it out below!). Though they admit more robust diagnostic trials are needed to further refine our approach to diagnosing “the great imitator” at each different stage, I will continue to follow the CDC guidelines and keep my index of suspicion high in at-risk populations.

Source
Operating Characteristics of Diagnostic Tests for Syphilis. Acad Emerg Med. 2024 Sep 6; 00:1-3. doi: 10.1111/acem.15008. PMID: 39239836.