A 32-year-old man presents with a painless ulcer on the glans penis for 3 weeks. Dark-field microscopy shows motile spirochetes. His partner develops a maculopapular rash involving the palms and soles 8 weeks later. Which single feature best distinguishes primary syphilis from secondary syphilis?

## Distinguishing Primary from Secondary Syphilis ### Clinical Presentation Timeline **Primary Syphilis** occurs 3–90 days after inoculation and is characterized by a **solitary, painless ulcer (chancre)** at the site of spirochete entry. This is the hallmark discriminating feature. **Secondary Syphilis** develops 4–10 weeks after the primary chancre appears (or while it is still healing) and is a **systemic manifestation** with widespread mucocutaneous lesions, including the classic involvement of palms and soles. ### Why the Correct Answer is "Solitary lesion at site of inoculation" **Key Point:** The **solitary chancre** is the pathognomonic finding of primary syphilis. It is: - Painless (unlike herpes or haemophilus) - Indurated with a clean base - Associated with regional lymphadenopathy (non-suppurative) - Present at the exact site of inoculation This single lesion is the **best discriminator** because it is virtually diagnostic of primary syphilis and absent in secondary syphilis, which presents with **multiple lesions** distributed systemically. ### Why Other Options Are Not Discriminators | Feature | Primary Syphilis | Secondary Syphilis | Discriminating? | | --- | --- | --- | --- | | **Spirochetes on dark-field** | Present (early) | Present in lesions | **NO** — both may show spirochetes | | **Palms/soles involvement** | Absent | Present (classic) | **YES, but backwards** — this is secondary, not primary | | **Positive RPR/VDRL** | Positive (late primary) | Positive (always) | **NO** — both positive; secondary has higher titers | **Clinical Pearl:** The chancre may heal spontaneously even without treatment, leading to a false sense of cure. However, untreated primary syphilis progresses to secondary syphilis in ~25% of patients. **High-Yield:** Remember the **"4 Cs" of the primary chancre**: - **C**lean base - **C**artilagenous (indurated) - **C**ircinately shaped - **C**ontiguous with regional lymph nodes (epitrochlear, inguinal) **Mnemonic: VDRL-Positive-Both** — Venereal Disease Research Lab test is positive in both primary (late) and secondary syphilis, so it is NOT a discriminator.