Version 1.0 — Published July 2026
Quick Answer
STD dermatology image MCQs contribute 3-5 questions per NEET PG paper, straddling dermatology, community medicine, and microbiology. Five high-yield patterns recur reliably:
- Primary syphilis chancre — single, painless, indurated ulcer with clean base; painless bilateral discrete LN; dark-field microscopy for Treponema; VDRL/RPR plus FTA-ABS; benzathine penicillin 2.4 MU IM single dose
- Secondary syphilis — bilateral symmetric copper-red maculopapular rash INCLUDING palms and soles, condyloma lata, moth-eaten alopecia, snail-track oral ulcers; VDRL high-titre; benzathine penicillin
- Chancroid — multiple, painful, ragged, soft ulcers with undermined edges; painful matted unilateral suppurating buboes; Haemophilus ducreyi (school-of-fish Gram stain); azithromycin 1 g single dose
- LGV — small painless self-healing primary papule, THEN painful matted inguinal buboes with groove sign separated by inguinal ligament; Chlamydia trachomatis L1-L3; doxycycline 100 mg BD for 21 days
- Genital HSV — grouped painful vesicles on erythematous base becoming shallow ulcers with scalloped borders; Tzanck smear multinucleated giant cells; PCR gold-standard; acyclovir; suppressive therapy for 6 or more recurrences per year
Locking these 5 patterns plus 8-10 additional STI images (condyloma acuminata, molluscum, scabies, pediculosis pubis, granuloma inguinale) over 1-2 weeks moves accuracy from 40 to 85 percent in STI MCQs.
Why STI image MCQs are high-yield for NEET PG
STIs cluster across dermatology, microbiology, community medicine, and obstetrics. NEET PG, INI-CET, and FMGE feature genital ulcer disease as image MCQs because the ulcer characteristics — painful vs painless, single vs multiple, indurated vs soft, clean vs purulent base — and the associated lymphadenopathy pattern are stereotyped and clinically diagnostic. The India-specific epidemiology (over 30 million adults with active STI at any time per NACO estimates; syphilis and HSV-2 the commonest ulcerative STIs; chancroid declining but still endemic in migrant-worker corridors and northeast India; LGV re-emerging with MSM cohorts) adds a public-health flavour that NEET PG tests.
Drilling these 5 patterns plus 8-10 additional STI images over 1-2 weeks moves accuracy from 40 to 85 percent.
Foundational approach to genital ulcer disease
The 5-discriminator matrix
| Feature | Syphilis chancre | Chancroid | LGV | Genital HSV |
|---|
| Number | Single | Multiple | Single primary | Multiple grouped vesicles |
| Pain | Painless | Painful | Painless primary, painful bubo | Painful |
| Induration | Indurated | Soft | Small papule | Vesicles then shallow ulcer |
| Base | Clean | Purulent grey | Small self-healing | Shallow with scalloped border |
| Lymphadenopathy | Bilateral, painless, discrete, rubbery, non-suppurative | Unilateral, painful, matted, suppurative bubo | Matted painful bubo with groove sign | Bilateral tender |
| Organism | Treponema pallidum | Haemophilus ducreyi | Chlamydia trachomatis L1-L3 | HSV-2 (over 70 percent), HSV-1 |
| Incubation | 3 weeks (9-90 days) | 4-7 days | 3-30 days | 2-14 days |
| Diagnosis | Dark-field, VDRL, FTA-ABS | Gram stain (school-of-fish), culture | NAAT with LGV typing, CFT | HSV PCR, Tzanck, type-specific IgG |
| Treatment | Benzathine penicillin G 2.4 MU IM | Azithromycin 1 g PO OR ceftriaxone 250 mg IM | Doxycycline 100 mg BD for 21 d | Acyclovir/valacyclovir/famciclovir |
Pattern-recognition triggers
| Finding | First-line diagnosis | Confirmatory test |
|---|
| Single painless indurated ulcer with clean base | Primary syphilis | Dark-field, VDRL, FTA-ABS |
| Bilateral symmetric palm-sole rash plus condyloma lata | Secondary syphilis | VDRL high-titre, FTA-ABS |
| Multiple painful soft ulcers plus suppurating bubo | Chancroid | Gram stain, culture |
| Matted inguinal bubo with groove sign | LGV | NAAT with LGV typing |
| Grouped painful vesicles on erythematous base | Genital HSV | HSV PCR |
MCQ 1: 28-year-old man with a single painless genital ulcer 4 weeks after unprotected sex
Image description: [Clinical photograph of the glans penis of a 28-year-old man. The image shows a single, well-circumscribed, round ulcer approximately 1.2 cm in diameter on the coronal sulcus. The ulcer has raised, well-defined, indurated edges, a clean, red-pink, non-purulent base, and no visible slough. There is no surrounding erythema and no phimosis. A paired inset shows bilateral, discrete, rubbery, non-tender inguinal lymph nodes approximately 1.5-2 cm each. A dark-field microscopy inset panel shows motile spirochaetes — spiral organisms with characteristic corkscrew motility.]
Clinical vignette: A 28-year-old truck driver from a highway corridor in Uttar Pradesh presents to the district DSRC (Designated STI Clinic) with a painless ulcer on the tip of his penis noticed 5 days ago. He reports one episode of unprotected sex with a commercial sex worker approximately 4 weeks ago during a long-distance haul. He has no dysuria, no discharge, and no systemic symptoms. Married with two children; wife lives in the village. On examination — the ulcer as described, no phimosis, no urethral discharge, and bilateral rubbery non-tender inguinal lymph nodes.
Investigations: Dark-field microscopy of ulcer exudate — motile spirochaetes seen. VDRL 1:32 (positive quantitative titre). TPHA reactive. HIV ELISA — negative (to be repeated at 3 months window). HBsAg negative, HCV negative. Wife counselled and offered VDRL screening.
Options:
- (a) Primary syphilis with chancre
- (b) Chancroid
- (c) Genital herpes
- (d) Behcet disease
Correct answer: (a) Primary syphilis with chancre
Reasoning: A single, painless, indurated, clean-based ulcer with raised well-defined edges plus painless bilateral discrete non-suppurative inguinal lymphadenopathy is the textbook primary syphilis chancre. Incubation is 3 weeks (9-90 days range). Dark-field microscopy shows motile spirochaetes and is diagnostic. VDRL becomes positive 3-6 weeks after infection with a rising titre; TPHA (or FTA-ABS) becomes reactive earlier and stays positive lifelong. Chancroid ulcers are painful, multiple, soft, and purulent with matted unilateral suppurating buboes. Genital HSV presents as grouped painful vesicles. Behcet has recurrent oral plus genital ulcers plus uveitis plus systemic features.
Teaching pearl — primary syphilis treatment:
- First-line: benzathine penicillin G 2.4 million units IM single dose (1.2 MU in each buttock)
- Penicillin-allergic non-pregnant patients: doxycycline 100 mg twice daily for 14 days OR tetracycline 500 mg 4 times daily for 14 days
- Penicillin-allergic pregnant patients: desensitisation to penicillin and treat — no safe alternative for pregnancy
- Follow-up: clinical review at 3, 6, and 12 months; repeat quantitative VDRL/RPR at 3, 6, and 12 months; a 4-fold drop in titre by 6 months confirms treatment response
- Partner notification: all sexual contacts in the last 3 months (primary syphilis) tested and treated presumptively
- Jarisch-Herxheimer reaction: fever, rigors, myalgia, and rash worsening within 24 hours of first penicillin dose; endotoxin release from dying spirochaetes; managed with paracetamol and reassurance
- NEET PG tests the single-dose penicillin regimen and dark-field microscopy as key facts
MCQ 2: 32-year-old with a copper-red palm-sole rash and moist perianal plaques
Image description: [A composite clinical photograph: (panel 1) both palms of a 32-year-old man showing multiple bilateral symmetric copper-red maculopapular lesions approximately 5-10 mm in size, non-itchy, non-scaling, on the palms and thenar eminences. (panel 2) both plantar surfaces showing similar copper-red macules and papules involving the soles. (panel 3) perianal region showing broad, flat-topped, moist, grey-white plaques (condyloma lata) at intertriginous zone. (panel 4) oral cavity showing snail-track ulcers and mucous patches on the buccal mucosa. (panel 5) scalp showing patchy moth-eaten alopecia and the lateral eyebrow showing partial thinning.]
Clinical vignette: A 32-year-old graphic designer from Mumbai presents to the dermatology OPD with a non-itchy, non-painful reddish-brown rash all over his body for 3 weeks, most prominent on the palms and soles. He also describes a mild sore throat, mild fever, generalised malaise, and hair loss in patches for the same duration. He recalls a small painless sore on his penis approximately 3 months ago which resolved on its own without treatment. Unprotected sex with a new partner approximately 5 months ago. On examination — as described, plus generalised non-tender lymphadenopathy in cervical, axillary, and inguinal chains.
Investigations: VDRL 1:128 (very high titre). TPHA reactive. HIV ELISA — negative. LFT — mildly raised ALT (72 U/L). Urine — mild proteinuria. CBC — normal. HBsAg negative.
Options:
- (a) Secondary syphilis with palmoplantar rash, condyloma lata, and mucous patches
- (b) Pityriasis rosea
- (c) Guttate psoriasis
- (d) Drug reaction
Correct answer: (a) Secondary syphilis with palmoplantar rash, condyloma lata, and mucous patches
Reasoning: A bilateral symmetric non-itchy copper-red maculopapular rash INCLUDING palms and soles is a hallmark of secondary syphilis — few other exanthems consistently involve palms and soles (Rocky Mountain spotted fever, coxsackie hand-foot-mouth, drug reactions, meningococcaemia, atypical measles, and severe erythema multiforme). The combination with condyloma lata (broad, moist, highly infectious papules at intertriginous zones, distinct from the papillary condyloma acuminata of HPV), snail-track ulcers and mucous patches on the oral mucosa, moth-eaten alopecia including lateral eyebrow, generalised non-tender lymphadenopathy, and a recall history of a painless penile sore 3 months ago that resolved (the primary chancre) makes the diagnosis secondary syphilis. VDRL titre 1:128 is very high, consistent with secondary syphilis.
Pityriasis rosea has a herald patch followed by a Christmas-tree distribution on the trunk sparing palms and soles. Guttate psoriasis has small scaly papules on the trunk and extensor extremities. Drug reactions vary in morphology but rarely produce condyloma lata or snail-track ulcers.
Teaching pearl — secondary syphilis management:
- First-line: benzathine penicillin G 2.4 million units IM single dose (same as primary syphilis)
- Partner notification: all sexual contacts in the last 6 months (secondary syphilis) tested and presumptively treated
- HIV co-infection screening: essential; syphilis increases HIV transmission and vice versa; consider CD4 count in HIV-positive patients
- Follow-up: quantitative VDRL at 3, 6, 12, and 24 months; a 4-fold titre drop is expected; failure to drop = re-infection or treatment failure — investigate for neurosyphilis with LP
- Jarisch-Herxheimer reaction: more common in secondary than primary syphilis due to higher spirochaete burden
- Neurosyphilis workup: LP if neurological, ophthalmic, or auditory symptoms (headache, tinnitus, vision loss, cranial neuropathies, meningismus); CSF VDRL, cell count, protein; treat with IV crystalline penicillin G 18-24 MU/day for 10-14 days if positive
- NEET PG tests palmoplantar rash and condyloma lata as pattern-recognition pearls
MCQ 3: 24-year-old with multiple painful soft genital ulcers and a suppurating groin bubo
Image description: [Clinical photograph of the genital region of a 24-year-old man showing multiple painful ulcers on the shaft of the penis — 3 ulcers ranging 5-15 mm each, with ragged undermined edges, soft (non-indurated) borders, and a grey-yellow purulent base with slough. A paired inset shows a large fluctuant unilateral left inguinal lymph node approximately 3 cm with overlying erythema and a small draining sinus with purulent discharge. A Gram-stain microscopy inset panel shows short Gram-negative rods arranged in parallel "school-of-fish" or "railroad track" pattern.]
Clinical vignette: A 24-year-old migrant labourer from Assam presents to the district DSRC with painful sores on the penis for 10 days and a painful swelling in the left groin for 5 days. He has had unprotected sex with 2 partners in the past month. He describes the groin lump as increasingly painful and warm, and last night he noticed pus discharging from a small opening in the skin. He is otherwise well, no fever, no systemic symptoms. On examination — as described, plus unilateral tender matted inguinal lymph node with a discharging sinus.
Investigations: Gram stain of ulcer exudate — Gram-negative rods in school-of-fish arrangement. Chocolate agar culture — Haemophilus ducreyi grown after 48 hours (fastidious). Dark-field microscopy negative for Treponema. VDRL non-reactive (repeat at 6 weeks). HSV PCR negative. HIV ELISA — reactive; confirmatory Western blot pending; CD4 count 480.
Options:
- (a) Chancroid with suppurative bubo, plus HIV co-infection
- (b) LGV
- (c) Granuloma inguinale (Donovanosis)
- (d) Primary syphilis
Correct answer: (a) Chancroid with suppurative bubo, plus HIV co-infection
Reasoning: Multiple painful ulcers with ragged undermined soft edges and a purulent grey-yellow base, plus a painful unilateral suppurating matted inguinal bubo, plus Gram stain showing school-of-fish Gram-negative rods = chancroid caused by Haemophilus ducreyi. Chancroid is endemic in migrant-worker corridors and northeast India, has an incubation of 4-7 days, and is a major cofactor for HIV transmission — hence the strong recommendation to screen every chancroid patient for HIV.
LGV also causes matted painful buboes but the primary lesion is a small painless self-healing papule, not multiple painful ulcers; and LGV buboes show the groove sign separating femoral and inguinal nodes across the inguinal ligament. Granuloma inguinale (Donovanosis, Klebsiella granulomatis) produces painless beefy-red granulomatous ulcers with rolled edges and no lymphadenopathy (pseudobuboes may occur); Giemsa stain shows Donovan bodies inside macrophages. Primary syphilis has a single painless indurated ulcer.
Teaching pearl — chancroid treatment:
- First-line: azithromycin 1 g PO single dose OR ceftriaxone 250 mg IM single dose
- Alternatives: ciprofloxacin 500 mg twice daily for 3 days OR erythromycin 500 mg 4 times daily for 7 days (used in pregnancy)
- Bubo drainage: aspirate through healthy skin if fluctuant; incision and drainage may cause chronic sinuses
- HIV screening: mandatory — over 10 percent of chancroid patients are HIV-positive; chancroid is a strong HIV cofactor
- Partner notification: all sexual contacts in the last 10 days tested and presumptively treated
- Follow-up: clinical review at 3-7 days for ulcer response; slower response in HIV-positive patients
- NEET PG tests painful multiple soft ulcers plus school-of-fish Gram stain as the key clues
MCQ 4: 30-year-old MSM with a painful matted inguinal bubo and a linear depression across the inguinal ligament
Image description: [Clinical photograph of the inguinal region of a 30-year-old man showing a large matted, painful, unilateral inguinal lymph node mass approximately 5 cm with overlying erythema and induration. A distinctive linear depression (groove sign) is visible across the mass, running along the line of the inguinal ligament, dividing the mass into a smaller superior (inguinal) and a larger inferior (femoral) component. Two draining sinuses are visible at the surface. There is no primary genital ulcer visible on the shaft or glans of the penis (the primary lesion resolved earlier and was unnoticed).]
Clinical vignette: A 30-year-old man who has sex with men (MSM) presents to a metro STI clinic with a painful swelling in the left groin for 3 weeks, becoming increasingly matted and tender. He recalls a small painless bump on the penis 5-6 weeks ago that resolved without treatment. He denies discharge but describes rectal discomfort and occasional mucous per rectum for 2 weeks. Sexual history — receptive anal intercourse with multiple male partners over the past 6 months.
Investigations: NAAT of ulcer swab and rectal swab — Chlamydia trachomatis positive; LGV typing (serovars L1-L3) positive. Complement fixation titre 1:256 (markedly positive; over 1:64 is supportive of LGV). HIV ELISA — negative. Syphilis VDRL — non-reactive. HSV PCR — negative. Gram stain — no organisms. HBsAg negative. Anoscopy — proctitis with mucosal ulceration.
Options:
- (a) LGV with groove sign
- (b) Chancroid
- (c) Non-LGV chlamydial infection
- (d) Hidradenitis suppurativa
Correct answer: (a) LGV with groove sign
Reasoning: A painful matted inguinal bubo with a groove sign (linear depression running along the inguinal ligament separating the femoral and inguinal node groups), combined with a recall history of a self-healing painless penile papule 5-6 weeks earlier, plus proctitis in a receptive MSM, is textbook LGV. LGV is caused by Chlamydia trachomatis serovars L1, L2, and L3 — distinct from the D-K serovars causing genital chlamydia. NAAT with LGV typing on ulcer or rectal swab is diagnostic; complement fixation titres greater than 1:64 support the diagnosis.
The groove sign appears in about a third of LGV cases and is highly suggestive but not pathognomonic — some chancroid buboes may look similar but do not typically show the sharp linear division. Non-LGV chlamydial infection (serovars D-K) causes urethritis, cervicitis, and PID but not matted buboes. Hidradenitis suppurativa causes recurrent painful nodules and sinuses in intertriginous zones (axilla, groin, buttocks) but no primary genital ulcer.
Teaching pearl — LGV treatment and stages:
- First-line: doxycycline 100 mg twice daily for 21 days — the extended duration is essential to prevent late tertiary complications
- Alternatives: erythromycin 500 mg 4 times daily for 21 days (used in pregnancy)
- Bubo aspiration: through healthy skin if fluctuant to prevent chronic sinuses
- Partner notification: all sexual contacts in the past 60 days tested and treated presumptively
- Tertiary LGV (untreated for months to years) — genito-anorectal syndrome with proctocolitis, rectal strictures, fistulas, elephantiasis (esthiomene), vulval elephantiasis in women; surgical management for strictures
- HIV-LGV co-infection — increasing MSM cohort; longer treatment duration and closer follow-up
- NEET PG tests groove sign and doxycycline 21 days as key facts
MCQ 5: 22-year-old with grouped painful vesicles on the vulva 5 days after unprotected sex
Image description: [Clinical photograph of the vulva of a 22-year-old woman showing multiple, small (2-4 mm), grouped vesicles on an erythematous base on the labia majora and labia minora bilaterally. Some vesicles have ruptured to form shallow, painful, well-circumscribed ulcers with scalloped or polycyclic borders. There is marked surrounding erythema and mild oedema. A paired inset shows bilateral tender inguinal lymphadenopathy approximately 2 cm each. A Tzanck-smear microscopy inset panel shows multinucleated giant cells with intranuclear inclusions.]
Clinical vignette: A 22-year-old college student presents to the gynaecology OPD with painful genital sores, difficulty passing urine, fever, and generalised malaise for 5 days. She had unprotected sex with a new partner approximately 7-10 days ago. This is her first episode. She reports intense pain and burning, especially when urinating (dysuria), and has had to use a bucket to pass urine because of the pain. She also describes tingling and burning in the vulva 1 day before the vesicles appeared. On examination — grouped painful vesicles on erythematous base on the vulva, shallow ulcers with scalloped borders, marked erythema, oedema, and tenderness. Bilateral tender inguinal lymphadenopathy. Temperature 38.4, mildly tachycardic.
Investigations: HSV PCR of lesion swab — HSV-2 positive. Tzanck smear — multinucleated giant cells with intranuclear inclusions. HSV-2 IgG — negative on presentation (will seroconvert at 6-12 weeks). VDRL — non-reactive. Chancroid Gram stain — negative. HIV ELISA — negative.
Options:
- (a) Primary genital herpes (HSV-2)
- (b) Recurrent genital herpes
- (c) Chancroid
- (d) Fixed drug eruption
Correct answer: (a) Primary genital herpes (HSV-2)
Reasoning: Grouped painful vesicles on an erythematous base evolving to shallow painful ulcers with scalloped borders, bilateral tender inguinal lymphadenopathy, systemic symptoms (fever, malaise, dysuria), and a prodromal tingling sensation 1 day before the vesicles appeared, in a young woman with recent unprotected sex — this is a first-episode primary genital HSV infection. The absence of HSV-2 IgG on presentation (which will seroconvert at 6-12 weeks) confirms this is a primary and not a recurrent episode. HSV PCR is the gold-standard confirmatory test; Tzanck smear showing multinucleated giant cells with intranuclear inclusions supports the diagnosis but has lower sensitivity than PCR.
Recurrent HSV episodes are milder, unilateral or localised, without systemic symptoms, and occur in previously seropositive patients. Chancroid ulcers are non-vesicular, more purulent, and often unilateral suppurating buboes. Fixed drug eruption may cause localised painful vesicles or bullae but the drug history and recurrence at the same site are the clues.
Teaching pearl — genital HSV management:
- Primary episode treatment: acyclovir 400 mg TDS for 7-10 days OR valacyclovir 1 g BD for 7-10 days OR famciclovir 250 mg TDS for 7-10 days
- Recurrent episode treatment (episodic): acyclovir 400 mg TDS for 5 days OR valacyclovir 1 g BD for 3 days OR famciclovir 250 mg TDS for 5 days
- Suppressive therapy (offered if 6 or more recurrences per year): acyclovir 400 mg BD long-term OR valacyclovir 500 mg OD OR famciclovir 250 mg BD; reduces recurrence by 70-80 percent and asymptomatic viral shedding
- Supportive care: analgesia (paracetamol, topical lidocaine gel), warm sitz baths, catheter for severe dysuria and retention
- Pregnancy: first-episode HSV in the third trimester or peripartum is a strong indication for elective caesarean section to prevent neonatal HSV (mortality 30-50 percent even with treatment); suppressive acyclovir 400 mg TDS from 36 weeks reduces recurrence at delivery
- Partner notification and counselling: type-specific serology for partners; asymptomatic shedding contributes to transmission; condoms reduce but do not eliminate risk
- HIV screening: mandatory; HSV-2 is a major cofactor for HIV acquisition
- NEET PG tests grouped vesicles, Tzanck smear, and acyclovir dose
Common pitfalls in STI dermatology image MCQs
Five frequent error patterns appear in NEET PG STI questions.
Pitfall 1: Chancre vs chancroid confusion
The exam favourite. Chancre — painless, single, indurated, clean base, bilateral discrete rubbery non-suppurative LN, Treponema pallidum. Chancroid — painful, multiple, soft, purulent base, unilateral matted suppurating bubo, Haemophilus ducreyi. The five discriminators — painless vs painful, single vs multiple, indurated vs soft, clean vs purulent, LN pattern — are asked directly.
Pitfall 2: Missing the palm-and-sole clue in secondary syphilis
Few exanthems consistently involve palms and soles. Any rash question with palm-and-sole involvement should trigger the differential: secondary syphilis, Rocky Mountain spotted fever, coxsackie hand-foot-mouth (usually children), meningococcaemia, drug reactions, atypical measles, erythema multiforme. In an adult with recent unprotected sex and no other systemic features, secondary syphilis is the top pick.
Pitfall 3: Confusing condyloma lata with condyloma acuminata
Condyloma lata — SECONDARY SYPHILIS — broad, moist, flat-topped, grey-white plaques, highly infectious, seen at intertriginous zones. Condyloma acuminata — HPV — dry papillary cauliflower-like lesions, non-purulent, seen at genital or perianal sites. Both are "genital warts" in lay language but are entirely different diseases with different treatments (penicillin vs podophyllin/imiquimod/cryotherapy).
Pitfall 4: Missing the groove sign in LGV
The groove sign — a linear depression across the inguinal ligament separating the enlarged femoral and inguinal node groups — appears in about a third of LGV cases and is highly suggestive. In an MSM presenting with matted painful buboes plus proctitis, LGV should be the top pick even without a primary ulcer (which often resolves unnoticed).
Pitfall 5: Confusing Donovanosis (granuloma inguinale) with LGV
Donovanosis (Klebsiella granulomatis) — beefy-red, painless, granulomatous ulcers with rolled edges, easy contact bleeding, no true lymphadenopathy (pseudobuboes may occur — subcutaneous granulomas that look like nodes), Donovan bodies in macrophages on Giemsa stain. Treatment — azithromycin 1 g weekly for at least 3 weeks OR doxycycline 100 mg BD for at least 3 weeks. LGV (Chlamydia L1-L3) — small painless self-healing papule, matted painful bubo with groove sign, proctitis in MSM, NAAT positive. Both are ulcerative STIs but Donovanosis is a beefy-red painless spreading ulcer while LGV is a small papule plus a bubo.
How to study STI dermatology for NEET PG
- Memorise the 5-discriminator matrix cold — chancre vs chancroid vs LGV vs granuloma inguinale vs HSV in a single table
- Review 8-10 additional STI image PYQs — condyloma acuminata (HPV cauliflower papilloma), condyloma lata (secondary syphilis moist plaque), molluscum contagiosum (umbilicated papules), pediculosis pubis (crabs), scabies of the genitals (burrows, itching worse at night), extragenital herpetic whitlow, gonococcal urethritis with discharge
- Pair images with the causative organism and its stain/PCR — Treponema pallidum on dark-field, Haemophilus ducreyi on Gram stain (school-of-fish) and chocolate agar, Chlamydia trachomatis L1-L3 on NAAT, HSV on PCR (or Tzanck for multinucleated giant cells), Klebsiella granulomatis with Donovan bodies on Giemsa
- Learn the treatment reflex — chancre and secondary syphilis: benzathine penicillin 2.4 MU IM single dose. Chancroid: azithromycin 1 g PO single dose. LGV: doxycycline 100 mg BD for 21 days. Genital HSV: acyclovir 400 mg TDS. Donovanosis: azithromycin 1 g weekly or doxycycline 100 mg BD for 3 weeks minimum
- Use spaced repetition — 1d, 3d, 7d, 14d, 30d review of the same 20-25 high-yield STI images
- Practice with NEETPGAI's daily image MCQ mode and drill 15-20 STI images per day for 1 week
Key takeaways
- STI dermatology contributes 3-5 questions per NEET PG paper
- Primary syphilis chancre — single painless indurated clean-based ulcer; benzathine penicillin 2.4 MU IM
- Secondary syphilis — bilateral symmetric palm-and-sole rash plus condyloma lata plus mucous patches
- Chancroid — multiple painful soft purulent ulcers with unilateral suppurating bubo; Haemophilus ducreyi; azithromycin 1 g
- LGV — painless self-healing primary papule THEN painful matted bubo with groove sign; Chlamydia L1-L3; doxycycline 21 days
- Genital HSV — grouped painful vesicles on erythematous base with scalloped-border ulcers; acyclovir; suppressive if 6 or more recurrences per year
- Always screen for HIV, hepatitis B and C, and syphilis in any STI patient
- Partner notification and treatment are mandatory
- India — NACO DSRC clinics, syndromic kits, and free treatment
Frequently Asked Questions
How is primary syphilis (chancre) distinguished from chancroid on clinical grounds?
The chancre-vs-chancroid distinction is a perennial NEET PG favourite. Primary syphilis (chancre) is caused by Treponema pallidum and appears 3-6 weeks after inoculation as a single, painless, indurated, round or oval ulcer with a clean base and raised well-defined edges, at the site of inoculation — glans penis, coronal sulcus, labia, cervix, anal margin, or oral mucosa. The associated inguinal lymphadenopathy is bilateral, discrete, rubbery, painless, and non-suppurative. Diagnosis is by dark-field microscopy of ulcer exudate (motile spirochaetes) or direct fluorescent antibody test, plus non-treponemal serology (VDRL or RPR) and treponemal serology (FTA-ABS or TPHA). Treatment is single-dose IM benzathine penicillin G 2.4 million units. Chancroid is caused by Haemophilus ducreyi and appears 4-7 days after inoculation as multiple, painful, non-indurated (soft) ulcers with ragged undermined edges and a purulent grey-yellow base. Associated inguinal lymphadenopathy is unilateral, painful, matted, and suppurates in 50 percent to form a fluctuant bubo. Diagnosis is by Gram stain (school-of-fish arrangement of Gram-negative rods) and chocolate-agar culture; PCR increasingly available. Treatment is azithromycin 1 g single dose OR ceftriaxone 250 mg IM single dose OR ciprofloxacin 500 mg twice daily for 3 days. The five discriminators to memorise are painless vs painful, single vs multiple, indurated vs soft, clean base vs purulent, bilateral non-suppurative LN vs unilateral suppurative bubo.
What are the classical features of secondary syphilis?
Secondary syphilis appears 4-10 weeks after the primary chancre resolves (untreated), driven by systemic haematogenous spread of Treponema pallidum. The hallmark is a bilateral symmetric non-pruritic maculopapular rash that classically involves the palms and soles — a strong differentiator from most other exanthems. The rash is copper-red or ham-coloured, non-vesicular, and self-resolves in weeks. Other characteristic features are condyloma lata (broad, moist, flat-topped papules and plaques at intertriginous sites — perianal, vulval, axillary — highly infectious), mucous patches and snail-track ulcers on oral, tongue, and genital mucosa, patchy moth-eaten alopecia of the scalp and lateral eyebrow, generalised non-tender lymphadenopathy, mild constitutional symptoms (low-grade fever, malaise, arthralgia), hepatitis, glomerulonephritis, and rarely uveitis or meningitis. Non-treponemal serology (VDRL, RPR) is strongly positive in secondary syphilis (over 95 percent sensitivity) with high titres (1:32 or more); treponemal serology (FTA-ABS, TPHA) is confirmatory. Treatment is single-dose IM benzathine penicillin G 2.4 million units. A Jarisch-Herxheimer reaction may follow first-dose treatment — fever, rigors, myalgia, and rash worsening in 24 hours due to endotoxin release from dying spirochaetes; managed with paracetamol and reassurance.
What is the groove sign of LGV and how is it distinguished from chancroid?
Lymphogranuloma venereum (LGV) is caused by Chlamydia trachomatis serovars L1, L2, and L3 — a distinct set from the D-K serovars causing genital chlamydia and the A-C serovars causing trachoma. LGV has three clinical stages. Stage 1 (primary) — a small, painless, self-healing papule, ulcer, or vesicle at the inoculation site, often unnoticed. Stage 2 (secondary, 2-6 weeks later) — painful matted inguinal lymphadenopathy with a characteristic groove sign — the enlarged femoral and inguinal nodes are separated by the inguinal ligament creating a linear depression, seen in about a third of cases and highly suggestive. Suppurating buboes rupture through multiple sinuses. Stage 3 (tertiary, months to years) — genito-anorectal syndrome with proctocolitis, strictures, fistulas, elephantiasis of the vulva or scrotum (esthiomene), and rectal stenosis. Diagnosis is by nucleic acid amplification test (NAAT) on ulcer swab or rectal swab with LGV-specific typing; complement fixation titres greater than 1:64 support the diagnosis. Treatment is doxycycline 100 mg twice daily for 21 days. LGV differs from chancroid in that the primary lesion is painless and often missed, the buboes typically show the groove sign (chancroid buboes do not), and the causative organism is Chlamydia not Haemophilus. NEET PG tests the groove sign as a pattern-recognition pearl and doxycycline 21 days as the treatment.
What is the difference between genital HSV primary and recurrent episodes?
Genital herpes is most commonly caused by HSV-2 (over 70 percent) and less commonly by HSV-1 (increasing globally due to oral-genital transmission). Primary genital HSV, the first episode in a person previously seronegative for HSV, is typically severe — grouped painful vesicles on an erythematous base progress to shallow, painful ulcers with scalloped or polycyclic borders; extensive labial, penile, perianal, and inner-thigh involvement; painful bilateral tender inguinal lymphadenopathy; systemic symptoms (fever, malaise, myalgia, dysuria, urinary retention in severe vulvar disease); lesions last 2-3 weeks and shed virus for 12 days. Recurrent episodes are less severe — prodromal tingling or burning for 1-2 days precedes localised clustered vesicles (often the same anatomical site), lesions last 5-10 days, systemic symptoms are mild or absent, and viral shedding lasts 4-5 days. Diagnosis is clinical plus HSV PCR of lesion swab (gold standard, replacing Tzanck smear and culture); Tzanck smear shows multinucleated giant cells but is less sensitive; type-specific serology (HSV-1 IgG, HSV-2 IgG) supports diagnosis and identifies prior infection. Treatment — episodic: acyclovir 400 mg three times daily for 5 days OR valacyclovir 1 g twice daily for 3 days OR famciclovir 250 mg three times daily for 5 days. Suppressive therapy is offered if 6 or more recurrences per year — acyclovir 400 mg twice daily long-term, valacyclovir 500 mg once daily, or famciclovir 250 mg twice daily. NEET PG tests grouped vesicles on erythematous base, Tzanck smear, and the acyclovir dose.
How is genital ulcer disease worked up systematically in an Indian STI clinic?
Genital ulcer disease work-up in India follows a structured syndromic and etiologic approach. Step 1 — history: sexual history (partners, protection, orientation, commercial sex work), duration, pain, single vs multiple lesions, previous STIs, HIV status. Step 2 — examination: characterise ulcer (size, edges, base, induration, tenderness, floor), regional lymph nodes (unilateral vs bilateral, painful vs painless, matted, suppurative, groove sign), extragenital involvement (oral, anal, palms, soles), skin rash, mucous patches, condyloma lata. Step 3 — laboratory: dark-field microscopy or PCR for T. pallidum from ulcer exudate; non-treponemal serology (VDRL or RPR — quantitative titre); treponemal serology (TPHA or FTA-ABS — confirmatory); HSV PCR on ulcer swab; Gram stain and chocolate agar culture for H. ducreyi if chancroid suspected; NAAT for Chlamydia trachomatis with LGV typing if painful matted buboes; HIV screening (ELISA); Hepatitis B and C serology; syphilis and HIV screening for all sexual partners. Step 4 — treatment: syndromic treatment while awaiting confirmation (WHO and NACO guidance) — benzathine penicillin G 2.4 million units IM (syphilis) plus azithromycin 1 g (chancroid), plus acyclovir if HSV suspected. Step 5 — partner notification and counselling — mandatory. Step 6 — HIV pre-test and post-test counselling; if HIV-positive, refer to ART centre. Step 7 — repeat serology at 3 and 6 months to document treatment response and rule out reinfection. The Indian National AIDS Control Organisation (NACO) provides free syndromic STI kits through DSRC (designated STI clinics) at district hospitals — NEET PG expects familiarity with syndromic management and the NACO framework.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Written by: NEETPGAI Editorial Team
Reviewed by: Pending SME Review
Last reviewed: July 2026
