A patient with secondary syphilis (diffuse maculopapular rash including palms and soles, VDRL reactive 1:64) is treated with benzathine penicillin G 2.4 MU IM single dose. When should post-treatment VDRL be repeated to confirm adequate serological response?

• A At 2 weeks post-treatment (most serological cure occurs within 2 weeks)
• B At 5 years post-treatment (VDRL stays elevated for years and only resolves after 5 years)
• C Repeat VDRL is unnecessary — TPHA is used for treatment response monitoring
• D At 6 and 12 months after treatment (fourfold or greater decline in titre confirms adequate response) ✓

Explanation

Following treatment of secondary syphilis, non-treponemal titres (VDRL/RPR) should be repeated at 6 and 12 months; the expected response is a fourfold (two-dilution) decrease in titre (e.g., 1:64 → 1:16). Failure to decline fourfold by 6 months suggests treatment failure or re-infection and necessitates CSF evaluation and retreatment. Treponemal tests (TPHA, FTA-ABS) remain positive for life and are NOT used to monitor treatment response. Complete VDRL seroreversion may take 1–2 years for secondary syphilis.

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

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