Secondary Syphilis
Infectious Disease
Illness script · Infectious Disease
Secondary Syphilis
Systemic dissemination of Treponema pallidum 4–10 weeks after primary infection, classically causing a diffuse rash including palms and soles.
This illness script for Secondary Syphilis covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- MSM (men who have sex with men) highest risk group
- Multiple sexual partners or unprotected intercourse
- HIV co-infection markedly increases risk
- Young adults aged 20–35 most commonly affected
- Concomitant STI (e.g., gonorrhea) increases susceptibility
02
Presentation
- Diffuse maculopapular rash — classically involves palms AND soles (key hallmark)
- Rash is non-pruritic; helps distinguish from most viral exanthems
- Condylomata lata — flat, moist, highly infectious warty plaques in intertriginous areas
- Mucous patches — painless gray-white plaques on oral/genital mucosa
- Constitutional symptoms: fever, malaise, sore throat, diffuse lymphadenopathy
- Patchy 'moth-eaten' alopecia of scalp or eyebrows
03
Pathophysiology
- T. pallidum spirochetes disseminate hematogenously from primary chancre
- Spirochetemia triggers systemic immune response and multiorgan seeding
- Immune complex deposition drives skin and mucous membrane lesions
- Not treated primary syphilis inevitably progresses to secondary stage
04
Diagnostics
- Screening: non-treponemal test (RPR or VDRL) — titers correlate with disease activity
- Confirmatory: treponemal test (FTA-ABS, TP-PA) — remains positive for life
- RPR titer classically very high (>1:8) in secondary syphilis
- Pearl: prozone phenomenon — false-negative RPR if undiluted due to antibody excess; dilute sample
- Darkfield microscopy of condylomata lata/mucous patches can directly visualize spirochetes
05
Management
- First-line: Benzathine penicillin G 2.4 million units IM single dose
- Penicillin-allergic non-pregnant patients: doxycycline 100 mg PO BID × 14 days
- Pregnant patients: must desensitize and treat with penicillin (no alternatives)
- Warn about Jarisch-Herxheimer reaction — fever/chills within hours of first dose; treat with antipyretics, NOT a reason to stop antibiotics
- Follow-up RPR titers at 6 and 12 months — expect fourfold decline confirming cure
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Pityriasis rosea
PR spares palms/soles and has a herald patch; secondary syphilis involves palms and soles and is RPR-positive.
Drug eruption
Drug rash is typically pruritic; secondary syphilis rash is non-pruritic with positive serology and systemic symptoms.
Condylomata acuminata (HPV)
HPV warts are raised, verrucous, and dry; condylomata lata are flat, moist, and RPR-positive.
Infectious mononucleosis
Mono causes exudative pharyngitis and positive monospot; secondary syphilis has mucous patches, palm/sole rash, and positive RPR.
Keep reading
Full library- Seborrheic DermatitisChronic, relapsing inflammatory skin condition causing greasy, yellowish scales and erythema in sebaceous gland-rich areas.
- SepsisLife-threatening organ dysfunction caused by a dysregulated host response to infection (SOFA ≥2 change from baseline).
Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.