Syphilis questions are the ultimate “read every word” trap: the organism is the same, but the stage changes the exam, the rash, the symptoms, the contagiousness, the test results, and even what other diseases the question writer wants you to consider. Here’s a Q-bank style breakdown where we pick the right answer—and then earn extra points by crushing every distractor.
Clinical Vignette (Q-bank style)
A 28-year-old man presents with a diffuse rash that began on his trunk and now involves his palms and soles. He reports low-grade fever and malaise. He is sexually active with multiple partners and uses condoms inconsistently. He recalls a painless genital sore about 2 months ago that resolved without treatment. Physical exam shows generalized nontender lymphadenopathy and several flat, moist lesions in the perineal region. HIV test is pending.
Which of the following is the most likely diagnosis?
A. Primary syphilis
B. Secondary syphilis
C. Tertiary syphilis
D. Haemophilus ducreyi infection (chancroid)
E. Herpes simplex virus type 2 infection
Correct Answer: B. Secondary syphilis
This vignette screams secondary syphilis—the “systemic dissemination” stage.
Why it’s secondary syphilis (key clues)
- Rash involving palms/soles: classic board clue
- Constitutional symptoms (fever, malaise)
- Generalized lymphadenopathy
- Condylomata lata: flat, moist, highly infectious lesions in intertriginous areas
- History of painless chancre that resolved: fits progression from primary → secondary
High-yield organism facts (Step 1/2)
- Treponema pallidum
- Spirochete
- Too thin for Gram stain → visualized with dark-field microscopy (classically for chancre exudate)
- Has outer membrane with few surface proteins (immune evasion)
- Transmission: sexual contact, vertical (congenital)
- Jarisch–Herxheimer reaction can occur after treatment: fever, chills, myalgias from cytokine release due to lysis of spirochetes (treat supportively; don’t stop penicillin)
Testing: how the exam wants you to think
Syphilis serology is often presented as two-step:
| Test Type | Examples | What it detects | Use | Key caveat |
|---|---|---|---|---|
| Nontreponemal | VDRL, RPR | Anticardiolipin (“reagin”) Ab | Screening and monitoring treatment (titers fall) | False positives (pregnancy, SLE/APS, viral infections, malaria); prozone effect possible |
| Treponemal | FTA-ABS, TP-PA | Ab specific to T. pallidum | Confirmation | Often stays positive for life |
Stage note: Secondary syphilis typically has high nontreponemal titers (very testable).
Treatment (high yield)
- Penicillin G is the treatment of choice for all stages
- Primary/secondary/early latent: IM benzathine penicillin G
- Neurosyphilis: IV aqueous penicillin G
- Penicillin allergy:
- Nonpregnant, non-neuro: doxycycline is sometimes used
- Pregnancy or neurosyphilis → desensitize and give penicillin
Systematic Distractor Breakdown (Why each wrong answer is wrong)
A. Primary syphilis
What primary syphilis looks like
- Single painless chancre
- Firm, clean base with indurated border
- Regional (often inguinal) nontender lymphadenopathy
- Appears ~3 weeks after exposure; heals spontaneously in 3–6 weeks
Why it’s wrong here
- This patient’s chancre was in the past and resolved.
- Now he has systemic symptoms + palms/soles rash + condylomata lata, which are secondary, not primary.
Board pearl: Primary = local lesion; Secondary = systemic spread.
C. Tertiary syphilis
What tertiary syphilis looks like
- Occurs years after untreated infection
- Classic manifestations:
- Gummas (granulomatous lesions; can involve skin, bone)
- Cardiovascular syphilis: vasa vasorum endarteritis → ascending aortic aneurysm, aortic regurgitation
- Neurosyphilis (can occur at various times, but classically later): tabes dorsalis, dementia, Argyll Robertson pupil
Why it’s wrong here
- Timeline doesn’t fit: symptoms are a couple months after chancre.
- Rash + condylomata lata are secondary features, not tertiary.
- No neuro findings, no aneurysm/regurgitation clues, no destructive granulomas.
High-yield association: Tertiary cardiovascular syphilis = vasa vasorum obliteration → “tree-barking” of aorta on pathology.
D. Haemophilus ducreyi (chancroid)
What chancroid looks like
- Painful genital ulcer(s)
- “Soft” chancre: ragged edges, gray/yellow exudate, bleeds easily
- Painful inguinal lymphadenopathy that can suppurate (buboes)
Why it’s wrong here
- Patient’s prior ulcer was painless and self-resolved—more consistent with syphilis chancre.
- Chancroid does not classically cause the palms/soles rash or systemic disseminated findings seen here.
Step tip: “Painful ulcer + painful nodes” = chancroid until proven otherwise.
E. HSV-2 infection
What genital herpes looks like
- Painful vesicles that become shallow ulcers
- Often burning/tingling prodrome
- Tender lymphadenopathy can occur
- Can recur (reactivation), especially with stress/immunosuppression
Why it’s wrong here
- Herpes lesions are typically painful vesicles/ulcers, not a single painless chancre followed by systemic rash.
- HSV does not give the classic palms/soles rash with condylomata lata.
- The perineal lesions described are flat, moist (condylomata lata), not vesicular.
Clinical crossover (Step 2): If they mention aseptic meningitis with genital lesions, HSV-2 moves up your list.
Rapid “Stages of Syphilis” Table (memorize this)
| Stage | Timing | Key Findings | Infectious? | High-yield notes |
|---|---|---|---|---|
| Primary | ~3 weeks after exposure | Painless chancre, regional LAD | Yes | Spirochetes in lesion (dark-field) |
| Secondary | weeks–months | Palms/soles rash, mucous patches, condylomata lata, generalized LAD, fever | Very | Highest titers on RPR/VDRL |
| Latent | months–years | Asymptomatic | Early latent: yes; late latent: less | Serology positive |
| Tertiary | years | Gummas, aortitis/aneurysm, neurosyphilis | Not typically | Can cause devastating late disease |
| Congenital | birth/infancy | Snuffles, rash, hepatosplenomegaly (early); Hutchinson teeth, saddle nose (late) | — | Always treat pregnant patients with penicillin |
High-Yield Add-Ons the Exam Loves
1) Neurosyphilis: can show up in sneaky ways
- Tabes dorsalis: demyelination of dorsal columns → sensory ataxia, lightning pains, positive Romberg
- Argyll Robertson pupil: accommodates but doesn’t react to light (“prostitute pupil”)
- Diagnosis: CSF VDRL (specific), CSF pleocytosis/protein (supportive)
2) False positives and false negatives (testing traps)
- False positive RPR/VDRL: pregnancy, SLE, antiphospholipid syndrome, viral infections
- Prozone phenomenon (rare): very high Ab levels interfere with agglutination → falsely negative nontreponemal test (fixed by diluting sample)
3) Treatment reaction that mimics worsening infection
- Jarisch–Herxheimer after starting penicillin: fever/chills/hypotension, especially in secondary syphilis due to high burden
- Supportive care; it’s not an allergy
Takeaway Pattern Recognition
When you see palms/soles rash + systemic symptoms + condylomata lata, lock in secondary syphilis—then use the stem to actively eliminate look-alikes:
- Painful ulcer? Think HSV or chancroid.
- Years later with aneurysm/neuro findings? Think tertiary.
- Single painless ulcer with local nodes only? Think primary.
Frequently Asked Questions
How do you recognize secondary syphilis on a vignette?
Secondary syphilis is recognized by systemic dissemination after a prior painless chancre. Classic clues include a diffuse rash that involves the palms and soles, constitutional symptoms such as low-grade fever and malaise, generalized nontender lymphadenopathy, and condylomata lata, which are flat, moist, highly infectious lesions in intertriginous areas.
How do you tell primary syphilis from secondary syphilis?
Primary syphilis presents as a local lesion, while secondary syphilis reflects systemic spread. Primary syphilis classically causes a single painless chancre with a firm, clean base and regional nontender lymphadenopathy, appearing about 3 weeks after exposure and healing spontaneously. Secondary syphilis occurs weeks to months later with palms-and-soles rash, constitutional symptoms, generalized lymphadenopathy, and condylomata lata.
How do you distinguish syphilis from chancroid or HSV-2 genital lesions?
Syphilis is suggested by a painless chancre followed later by systemic findings, whereas chancroid and HSV-2 are typically painful. Chancroid from Haemophilus ducreyi causes painful genital ulcers with ragged edges, gray-yellow exudate, and painful inguinal nodes that may suppurate. HSV-2 usually causes painful vesicles or shallow ulcers, often with a burning or tingling prodrome and possible recurrences.
What tests are used for syphilis, and which ones stay positive?
Syphilis testing is commonly presented as a two-step process using nontreponemal and treponemal tests. VDRL and RPR are nontreponemal screening tests that detect anticardiolipin antibodies and are also used to monitor treatment because titers fall. FTA-ABS and TP-PA are treponemal confirmatory tests that detect antibodies specific to Treponema pallidum and often remain positive for life.
What is the treatment of choice for syphilis, and what happens after treatment?
Penicillin G is the treatment of choice for all stages of syphilis. Primary, secondary, and early latent syphilis are treated with intramuscular benzathine penicillin G, while neurosyphilis requires intravenous aqueous penicillin G. After treatment, a Jarisch-Herxheimer reaction can occur, causing fever, chills, and myalgias from cytokine release due to spirochete lysis; treatment is supportive and penicillin should not be stopped.