Cutaneous syphilis
Lues; lues maligna; Treponema pallidum infection; primary / secondary / tertiary syphilis
Syphilis is a multisystem infection caused by Treponema pallidum with a substantial cutaneous footprint. Once thought near-eliminated in the UK, syphilis incidence has risen sharply since the early 2000s, particularly in men who have sex with men. The classical three stages each have characteristic skin findings — primary chancre, the protean secondary rash (rightly called "the great imitator"), and the rare modern-day tertiary gummata. Lues maligna is a rare ulceronodular variant in HIV co-infection. UK practice screens with combined treponemal IgG/IgM and non-treponemal RPR / VDRL; benzathine penicillin G remains first-line therapy.
Primary syphilis
- Painless, indurated, well-demarcated ulcer (chancre) at the site of inoculation — usually genital, but also oral, anal or extragenital (fingers, lips).
- Develops 10–90 days (median 21 days) after inoculation.
- Regional lymphadenopathy.
- Self-resolves over 3–6 weeks even without treatment; this allows disease to enter the secondary stage.
- Differential — herpes simplex (painful, grouped vesicles), chancroid (painful, ragged border), traumatic ulcer, Behçet, fixed drug eruption, EQ, anal SCC, vulval SCC.
Secondary syphilis — the great imitator
- Develops 6 weeks to 6 months after primary infection.
- Generalised, non-itchy, copper-coloured maculopapular eruption — characteristically involving palms and soles.
- Other patterns — annular, lichenoid, pustular, alopecia ("moth-eaten"), condylomata lata (flat moist papules in flexures), mucous patches and "snail-track" oral ulcers.
- Constitutional — fever, malaise, lymphadenopathy, hepatitis, glomerulonephritis, meningitis.
- Lues maligna — rare ulceronodular variant in HIV co-infection; severe ulcerative crusted nodules; rapid progression.
- Major mimic of viral exanthems, drug eruption, pityriasis rosea, psoriasis, lichen planus, mycosis fungoides, paraneoplastic dermatomyositis, lupus.
Tertiary syphilis
- Develops years to decades after untreated infection.
- Cutaneous gummata — destructive granulomatous nodules / ulcers; rare in the antibiotic era.
- Nodular tertiary syphilis — grouped firm nodules with central healing.
- Cardiovascular syphilis (aortitis, aortic regurgitation) and neurosyphilis (general paresis, tabes dorsalis) often co-exist.
Diagnosis
- Serology — combined treponemal-specific test (EIA / CIA for IgG/IgM, or TPPA) plus non-treponemal test (RPR or VDRL).
- Treponemal tests remain positive lifelong; non-treponemal tests fall with successful treatment — used to monitor response (four-fold decline in titre = adequate response).
- Dark-field microscopy of chancre exudate — diagnostic of primary syphilis where available.
- Lesion PCR for T. pallidum.
- Lumbar puncture for CSF examination in neurological symptoms, HIV co-infection, ocular involvement, or tertiary disease.
- HIV testing and sexually-transmitted-infection screen in all cases.
Management
- Primary, secondary or early latent (< 1 year) — benzathine penicillin G 2.4 MU IM single dose.
- Late latent (> 1 year) or unknown duration / tertiary (non-neuro) — benzathine penicillin G 2.4 MU IM weekly × 3.
- Neurosyphilis or ocular / otic syphilis — IV benzylpenicillin 3–4 MU 4-hourly for 14 days, or procaine penicillin + probenecid.
- Penicillin allergy — doxycycline 100 mg BD for 14–28 days (early / late respectively); desensitisation preferred in pregnancy and neurosyphilis.
- Jarisch-Herxheimer reaction common 2–24 hours after first dose — fever, malaise, exacerbation of skin lesions; manage with antipyretics; not penicillin allergy.
- Treatment follow-up — serial RPR / VDRL at 3, 6 and 12 months; four-fold titre decline confirms adequate response.
- Contact tracing per local sexual-health pathway.
References
- BASHH UK national guideline on the management of syphilis 2024.
- CDC Sexually Transmitted Infections Treatment Guidelines.
- Stamm LV. Syphilis — re-emergence of an old foe. Microb Cell; 2016.
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