A 35-year-old man is found to have a positive treponemal test (TPPA positive) on screening but a negative VDRL. He has no history of syphilis treatment. Which scenario best explains this 'reverse algorithm' pattern?

• A Biological false positive treponemal test from SLE or malaria
• B Treated syphilis — TPPA always reverts to negative 1 year post-treatment
• C Primary syphilis before chancre formation; VDRL becomes positive after treponemal tests
• D Latent syphilis (early or late latent) — treponemal antibodies persist for life but VDRL may decline to negative in late latent; treat as late latent syphilis ✓

Explanation

A positive treponemal test (TPPA/TPHA) with negative VDRL, in the absence of documented prior treatment, is consistent with late latent syphilis or latent syphilis of unknown duration. Non-treponemal antibodies (VDRL/RPR) decline over years in untreated late latent syphilis and may reach non-reactive levels, while treponemal tests remain positive for life. This pattern also occurs after successful treatment, but history is negative here. Biological false positives occur for VDRL (non-treponemal), not for specific treponemal tests (TPPA). Management: quantitative RPR/VDRL plus CSF examination to exclude neurosyphilis, then benzathine penicillin G 2.4 MU IM weekly for 3 doses.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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