Pathology · single question
A 23-year-old sexually active patient presents with irritated mucosa of the lower lip. Which organism is MOST likely responsible?
Show answer and explanation
Correct answer: B. Treponema pallidum
In a sexually active young adult with irritated lower lip mucosa, Treponema pallidum (the causative agent of syphilis) must be considered. Primary syphilis presents as a painless chancre (firm, indurated ulcer) at the site of inoculation — which can occur on the lip or oral mucosa following oral-genital contact. This is an important differential for oral ulcers in sexually active patients. Diagnosis: NAAT or darkfield microscopy.
- A. ❌ HPV causes verrucae/condylomata — raised, warty lesions — not described here.
- B. ✅ CORRECT – Treponema pallidum (primary syphilis) should be on the differential for a sexually active patient with lip/oral mucosal lesions (painless chancre).
- C. ❌ HSV-1 causes painful vesicles/ulcers, often with prodrome — not typically described as irritated mucosa in a sexually active context without a history of recurrence.
- D. ❌ Candida presents as wipeable white plaques or erythema — not typically as a lip lesion in an otherwise healthy young adult.