A 28-year-old man presents with a painless genital ulcer with indurated edges and clean base. Dark-ground illumination (DGI) of the ulcer exudate shows motile spiral organisms. Which stage and causative organism is most consistent?
- A Primary syphilis; Treponema pallidum ✓
- B Secondary syphilis; Treponema pallidum
- C Chancroid; Haemophilus ducreyi
- D Herpes genitalis; Herpes simplex virus type 2
Explanation
The primary chancre of syphilis is a single, painless, indurated (button-hard) ulcer with clean base and serous discharge — the classical presentation of primary syphilis. Dark-ground illumination of fresh exudate shows Treponema pallidum as thin motile spiral organisms with characteristic cork-screw motility. DGI is the most sensitive test for primary syphilis before serological tests become positive. Chancroid (H. ducreyi) presents with a painful, soft, non-indurated ulcer with ragged undermined edges. Herpes presents with multiple painful vesicles that rupture to form shallow ulcers.
Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.