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-demarcated border, indurated edges, and a clean base with scanty serous discharge. Regional lymph nodes are enlarged, firm, and non-tender. Dark-field microscopy of the ulcer exudate shows motile spirochetes. The patient denies systemic symptoms. What is the most likely stage of syphilis?

## Clinical Diagnosis: Primary Syphilis ### Key Clinical Features **Key Point:** Primary syphilis is characterized by a single painless ulcer (chancre) at the site of inoculation, appearing 3–90 days (average 21 days) after exposure. ### Chancre Characteristics | Feature | Primary Syphilis Chancre | |---------|-------------------------| | **Number** | Single (usually) | | **Pain** | Painless | | **Border** | Well-demarcated, indurated | | **Base** | Clean, granulating, serous exudate | | **Discharge** | Scanty, serous | | **Regional nodes** | Firm, enlarged, non-tender (epitrochlear, inguinal) | | **Systemic symptoms** | Absent | | **Dark-field microscopy** | *Treponema pallidum* (motile spirochetes) | ### Diagnostic Confirmation **High-Yield:** Dark-field microscopy showing motile spirochetes is pathognomonic for primary syphilis. The organism appears as a corkscrew-shaped motile bacterium. **Clinical Pearl:** The chancre is often solitary and located at the site of sexual contact (glans penis in this case). Regional lymphadenopathy (bubo) is non-tender and firm, distinguishing it from suppurative lymphadenitis seen in other STIs like LGV. ### Why This Is Primary, Not Secondary - **No systemic manifestations:** Secondary syphilis presents with rash (including palms/soles), fever, lymphadenopathy, and mucous patches. - **Single ulcer:** Primary stage has one chancre; secondary stage has multiple lesions. - **Timing:** 3 weeks fits the primary stage window (3–90 days). ### Serological Correlation - **RPR/VDRL:** May be negative early (first 1–2 weeks); becomes positive as primary progresses. - **FTA-ABS/TP-PA:** Positive (treponemal test). - **Dark-field microscopy:** Positive (as in this case).