Syphilis Serological Scar — SCE Infectious Diseases MCQ

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ModerateSTIsSyphilis Serological ScarSCE Infectious Diseases

A 38-year-old HIV-positive man (CD4 420, VL <50 on ART) has a repeatedly reactive treponemal antibody test (TPHA positive) but RPR is consistently non-reactive. He has no symptoms of syphilis and was treated for syphilis 5 years ago. What does this serological pattern represent?

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Correct answer: A — Serological scar — previous treated syphilis with treponemal antibody persistence (TPHA remains positive lifelong in most people)

Following successful treatment of syphilis, non-treponemal tests (RPR/VDRL) typically decline and may become non-reactive. However, treponemal tests (TPHA, FTA-Abs, treponemal EIA/CMIA) usually remain reactive for life — this is a 'serological scar' reflecting immunological memory. A reactive treponemal test with non-reactive RPR in a previously treated patient does NOT indicate active infection. This is the expected serological pattern years after adequate treatment. No further treatment is needed unless RPR rises fourfold, suggesting reinfection.

Reference: BASHH 2019 – Syphilis guidelines; CDC 2021 – Syphilis interpretation