## Primary Syphilis: Site of Inoculation **Key Point:** The glans penis is the most common site of primary syphilis (chancre) in heterosexual males, accounting for approximately 60–70% of cases. ### Anatomical Basis The chancre develops at the site of inoculation of *Treponema pallidum* during sexual contact. In males, the glans and coronal sulcus are the most frequently exposed and traumatized areas during intercourse, making them the most vulnerable to spirochetal entry. ### Clinical Features of Primary Chancre - **Appearance:** Painless, indurated, well-demarcated ulcer with a clean base and raised borders - **Size:** Typically 5–15 mm in diameter (though can be larger) - **Duration:** Appears 3–90 days after exposure (average 21 days) - **Associated finding:** Regional lymphadenopathy (rubbery, non-suppurative) - **Serology:** Non-treponemal tests (RPR/VDRL) may be negative early; treponemal tests (FTA-ABS, TP-PA) become positive ### Other Sites of Primary Chancre (in order of frequency) | Site | Frequency in Males | Frequency in Females | | --- | --- | --- | | Glans/coronal sulcus | 60–70% | — | | Prepuce | 15–20% | — | | Shaft | 5–10% | — | | Cervix | — | 40–50% | | Labia majora | — | 25–30% | | Perineum/rectum | 5–10% (MSM) | 5–10% | **High-Yield:** Extragenital chancres (lip, tongue, anus, rectum) occur in 5–10% of cases and are often missed, leading to delayed diagnosis and transmission. **Clinical Pearl:** A painless genital ulcer with regional lymphadenopathy and dark-field microscopy showing motile spirochetes is pathognomonic for primary syphilis. The glans is the single most common location in heterosexual males. [cite:Park 26e Ch 31]
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