A 28-year-old man from Delhi presents with a painless ulcer on the glans penis for 3 weeks. On examination, the ulcer has a well-defined, indurated border with a clean base and scanty serous discharge. Regional lymph nodes are enlarged, firm, and non-tender. He denies systemic symptoms. RPR is negative, but FTA-ABS is positive. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Primary Syphilis ### Key Clinical Features **Key Point:** Primary syphilis presents with a **chancre** — a single, painless, indurated ulcer with a clean base and well-demarcated border, appearing 3–90 days (average 21 days) after exposure. ### Characteristic Findings in This Case | Feature | Finding | Significance | |---------|---------|---------------| | **Lesion type** | Painless ulcer with indurated border | Classic chancre morphology | | **Location** | Glans penis | Common site in males | | **Duration** | 3 weeks | Within typical incubation period | | **Regional nodes** | Firm, non-tender lymphadenopathy | Epitrochlear/inguinal involvement | | **Systemic symptoms** | Absent | Distinguishes from secondary stage | | **RPR** | Negative | Early stage; serology may lag clinical signs | | **FTA-ABS** | Positive | Specific treponemal test; becomes positive early | ### Serological Pattern in Primary Syphilis **High-Yield:** FTA-ABS (and TP-PA) become positive **before** non-treponemal tests (RPR/VDRL) in primary syphilis. This patient's positive FTA-ABS with negative RPR is typical of **early primary syphilis** (first 3–4 weeks). ### Differential Staging ```mermaid flowchart TD A[Syphilis Suspected]:::outcome --> B{Clinical Stage?}:::decision B -->|Single painless ulcer<br/>+ regional LAD<br/>No systemic symptoms| C[Primary Syphilis]:::action B -->|Rash + systemic symptoms<br/>Generalized LAD<br/>Mucous patches| D[Secondary Syphilis]:::action B -->|Asymptomatic<br/>Positive serology<br/>No clinical signs| E[Latent Syphilis]:::action B -->|Gummas, neurosyphilis<br/>Cardiovascular involvement<br/>Years after infection| F[Tertiary Syphilis]:::action C --> G[Chancre resolves<br/>in 3-6 weeks<br/>even untreated]:::outcome ``` ### Clinical Pearl **Clinical Pearl:** The chancre is **self-limited** — it heals spontaneously in 3–6 weeks even without treatment. Patients often delay seeking care because the lesion appears to resolve, but untreated infection progresses to secondary syphilis (4–10 weeks post-exposure). ### Why Not Other Stages? - **Secondary syphilis:** Presents 4–10 weeks post-exposure with systemic manifestations (fever, rash, generalized lymphadenopathy, mucous patches, condyloma lata). This patient has no rash or systemic symptoms. - **Tertiary syphilis:** Occurs years later with gummas, neurosyphilis, or cardiovascular involvement. Timeline and clinical presentation do not fit. - **Latent syphilis:** Asymptomatic stage with positive serology but no clinical signs. This patient has an active ulcer.