A 35-year-old male presents with a painless ulcer on the shaft of the penis with raised, indurated borders and a clean base. Non-tender bilateral inguinal lymphadenopathy is present. What is the diagnostic test of choice and first-line treatment?

Answer and explanation

Correct answer: C. Darkfield microscopy / Treponemal serology; Intramuscular Benzathine Penicillin G

  1. Step 1: A solitary painless ulcer with indurated borders and rubbery non-tender adenopathy (hard chancre) is pathognomonic for primary syphilis caused by Treponema pallidum.
  2. Step 2: Diagnosis is made by darkfield microscopy of chancre exudate or serologic testing (RPR/VDRL confirmed by FTA-ABS/TPPA).
  3. Step 3: First-line curative treatment is a single intramuscular injection of 2.4 million units of Benzathine Penicillin G.
Answer
Darkfield microscopy / Treponemal serology; Intramuscular Benzathine Penicillin G.
Why not the others: Painful vesicles with Tzanck smear are Herpes simplex; painful soft ulcer with purulent base is Chancroid (Haemophilus ducreyi).

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