A 28-year-old man from Mumbai presents with a painless ulcer on his penis for 3 weeks. On examination, the ulcer has a well-demarcated border, indurated edges, and a clean base. Regional lymph nodes are enlarged, non-tender, and rubbery. Serological testing shows negative RPR but positive FTA-ABS. What is the most likely stage of syphilis?

Explanation

## Clinical Diagnosis: Primary Syphilis ### Key Features of the Presentation **Key Point:** Primary syphilis is characterized by a single painless ulcer (chancre) at the site of inoculation, typically appearing 3–90 days after exposure. ### Chancre Characteristics | Feature | Description | | --- | --- | | **Appearance** | Painless, indurated ulcer with clean base | | **Border** | Well-demarcated, raised, indurated edges | | **Base** | Smooth, clean, non-purulent | | **Size** | Typically 1–2 cm (can be larger) | | **Location** | Site of inoculation (genitals, lips, anus, fingers) | | **Duration** | Self-limited; heals in 3–6 weeks even without treatment | ### Regional Lymphadenopathy (Bubo) **Clinical Pearl:** The presence of **painless, rubbery, non-suppurative regional lymphadenopathy** (bubo) is a hallmark of primary syphilis. Nodes are typically unilateral if the chancre is unilateral. ### Serological Pattern in Early Primary Syphilis **High-Yield:** The patient's **negative RPR but positive FTA-ABS** indicates: - **FTA-ABS (treponemal test):** Becomes positive early (within 1–2 weeks of chancre appearance) and remains positive for life. - **RPR (non-treponemal test):** May still be negative in the first 1–2 weeks of primary syphilis; becomes positive later as the infection progresses. This serological pattern is consistent with **very early primary syphilis** (treponemal antibodies present, but non-treponemal antibodies not yet developed). ### Why Not Other Stages? **Mnemonic: SYPHILIS Stages — "Sore, Systemic, Sleeping, Serious"** - **S**econdary: Rash, fever, lymphadenopathy, mucosal patches — systemic manifestations. Would have positive RPR. - **S**leeping (Latent): Asymptomatic; no clinical signs. Would have positive both RPR and FTA-ABS. - **S**erious (Tertiary): Gummas, cardiovascular, neurosyphilis — late manifestations (years later). ### Timeline Context **Key Point:** The 3-week duration and isolated ulcer with regional lymphadenopathy, in the absence of systemic symptoms, confirms primary syphilis rather than secondary (which requires 4–10 weeks and systemic features).