Distinguishing Syphilis Chancre from Chancroid Chancre
The syphilitic chancre is typically painless, indurated, and clean-based with a single ulcer, while the chancroid chancre is painful, soft, purulent, and often multiple with ragged undermined edges—but clinical diagnosis alone is unreliable, with classic presentations occurring in only 31-35% of cases. 1, 2
Key Clinical Differences
Syphilis Chancre (Primary Syphilis)
- Pain: Painless ulcer is the hallmark feature 1, 3
- Consistency: Indurated (firm) base—hence the term "ulcus durum" (hard chancre) 3, 4
- Appearance: Clean-based ulcer with well-defined borders 1, 2
- Number: Usually single, though atypical presentations with multiple ulcers can occur 3, 4
- Lymphadenopathy: Firm, non-tender, rubbery regional lymph nodes 3
- Healing: Resolves spontaneously without scarring in 3-6 weeks 3
Chancroid Chancre (Haemophilus ducreyi)
- Pain: Painful ulcer is characteristic 1, 5
- Consistency: Soft, non-indurated base—hence "soft chancre" or "ulcus molle" 5
- Appearance: Deep ulcer with purulent (pus-filled) base, ragged and undermined edges, highly inflamed borders 1, 5
- Number: Often multiple ulcers that may coalesce 5
- Lymphadenopathy: Tender, often unilateral inguinal nodes that may suppurate (form buboes with pus discharge) 1, 5
- Healing: Heals with scarring, especially in extensive cases 1
Critical Diagnostic Pitfall
The classic clinical presentations described above occur in only a minority of patients—31% sensitivity for syphilis, 34% for chancroid, making clinical diagnosis alone highly unreliable. 2 There is considerable overlap in clinical presentations, and 10% of patients with genital ulcers have co-infections with both T. pallidum and H. ducreyi or HSV. 1
Essential Laboratory Workup
Since clinical diagnosis is inaccurate, the CDC mandates specific testing for all genital ulcers: 1
- Darkfield microscopy or direct immunofluorescence for Treponema pallidum from ulcer exudate 1
- Serologic test for syphilis (VDRL or RPR) performed at least 7 days after ulcer onset 1
- Culture for Haemophilus ducreyi on special media (though sensitivity ≤80% even with optimal media) 1
- HSV culture or antigen test to exclude herpes 1
- HIV testing is mandatory, as both conditions are cofactors for HIV transmission 1
Pathognomonic Clinical Sign
The combination of a painful ulcer with tender inguinal adenopathy that progresses to suppurative (pus-forming) inguinal adenopathy is almost pathognomonic for chancroid. 1 This occurs in approximately one-third of chancroid patients and is rarely seen with syphilis. 1
Empiric Treatment When Diagnosis Unclear
When laboratory confirmation is unavailable or delayed, the CDC recommends: 1
- Treat for syphilis if diagnosis is uncertain
- Treat for both syphilis AND chancroid if the patient resides in a community where H. ducreyi is prevalent, especially when diagnostic capabilities are limited 1
- This dual approach is critical because even after complete diagnostic evaluation, at least 25% of genital ulcers have no laboratory-confirmed diagnosis 1
Geographic Considerations
Chancroid is endemic in certain U.S. areas and occurs in discrete outbreaks, while syphilis has broader geographic distribution. 1 Local epidemiology should guide empiric treatment decisions when diagnostic testing is delayed. 1