Correct Answer: B. Syphilis
The combination of a painless genital ulcer with non-tender inguinal lymphadenopathy is pathognomonic for primary syphilis (chancre). The chancre is the hallmark lesion of primary syphilis caused by Treponema pallidum (a spirochete). Key discriminating features: the ulcer is typically indurated, with a clean base and rolled edges, and critically—it remains painless despite its appearance. The regional lymph nodes (inguinal) are enlarged but characteristically non-tender, distinguishing syphilis from other STIs. This occurs 3–90 days after exposure (average 21 days). The painless nature is crucial: it reflects the organism's ability to evade acute inflammatory response initially. In India, syphilis remains a significant public health concern, particularly in high-risk populations. Diagnosis is confirmed by dark-field microscopy (seeing motile spirochetes), RPR/VDRL (non-treponemal), and FTA-ABS/TP-PA (treponemal tests). The DOC is benzathine penicillin G 2.4 MU IM single dose for primary syphilis per Indian STI guidelines. Early treatment prevents progression to secondary and tertiary syphilis.
Why the other options are wrong
A. Chancroid — Chancroid (caused by Haemophilus ducreyi) presents with a painful ulcer—the opposite of the clinical picture. The ulcer has a purulent base and ragged edges. Inguinal lymph nodes are tender and suppurative, often forming buboes. This is the key discriminator: pain is prominent in chancroid, whereas the question explicitly states painless ulcer. Chancroid is rare in India compared to syphilis. C. Herpes genitalis — Herpes simplex virus (HSV-1/HSV-2) causes painful vesicles and ulcers with severe pain, burning, and dysuria. The lesions are multiple, shallow, and preceded by prodromal symptoms (tingling, pain). Regional lymphadenopathy is present but is tender. The painless nature of the lesion in the question rules out herpes. Herpes also typically presents with systemic symptoms (fever, malaise) in primary infection. D. Granuloma inguinale — Granuloma inguinale (caused by Klebsiella granulomatis) presents with a beefy-red, painless ulcer that bleeds easily and is progressive. While the ulcer can be painless, the inguinal lymphadenopathy is absent or minimal—lymph nodes are typically not involved (unlike syphilis). The lesion is also more destructive and progressive. The combination of painless ulcer + prominent non-tender lymphadenopathy points to syphilis, not granuloma inguinale.
High-Yield Facts
- Chancre (primary syphilis): painless, indurated ulcer with clean base, rolled edges, and non-tender regional lymphadenopathy—the classic triad.
- Treponema pallidum is a spirochete; diagnosis via dark-field microscopy (motile organisms), RPR/VDRL, and FTA-ABS/TP-PA confirmatory tests.
- DOC for primary syphilis: benzathine penicillin G 2.4 MU IM single dose; penicillin allergy → doxycycline 100 mg BD × 14 days (per Indian STI guidelines).
- Painless ulcer + non-tender lymph nodes = syphilis; painful ulcer + tender lymph nodes = chancroid or herpes.
- Secondary syphilis (6–8 weeks later): maculopapular rash (including palms/soles), condyloma lata, mucous patches, generalized lymphadenopathy.
- Tertiary syphilis (years later): neurosyphilis, tabes dorsalis, general paresis of insane (GPI), gummas—preventable by early treatment.
Mnemonics
PAIN in STI ulcers Painful = Chancroid, Herpes; Apainless = syphilis, granuloma inguinale. Then add lymph node tenderness: syphilis has non-tender nodes (unlike chancroid/herpes). Chancre vs Chancroid Chancre (syphilis) = Clean, Calm, Cool (painless, non-tender nodes). Chancroid = Crude, Cruel, Crying (painful, tender buboes). One letter difference, opposite clinical picture.
NBE Trap
NBE pairs "painless ulcer" with multiple STIs but tests whether students recall that non-tender lymphadenopathy is the discriminating feature unique to syphilis. Students may incorrectly choose granuloma inguinale (which can have painless ulcers) if they forget that granuloma inguinale typically lacks significant lymphadenopathy.
Clinical Pearl
In Indian STI clinics, the "painless ulcer + non-tender nodes" triad is the bedside pearl that immediately triggers syphilis workup. Many patients delay seeking care because the painless chancre seems benign, allowing progression to secondary syphilis with systemic manifestations—early recognition and penicillin therapy prevent this cascade.
_Reference: Robbins Ch. 8 (Infectious Diseases); Harrison Ch. 195 (Syphilis); KD Tripathi Ch. 47 (Antibiotics & STIs)_