Syphilis

Pathogenesis and Tissue Invasion

Structure of the Spirochete and Immune Evasion

• Treponema pallidum is a spiral-shaped bacterium that moves using internal flagella (endoflagella). Its outer membrane lacks the typical lipopolysaccharide (LPS) endotoxin, which lets it slip past the innate immune system largely unnoticed, earning it the label of a "stealth pathogen."
• It has a strong affinity for vascular endothelial cells and triggers perivascular inflammation dominated by plasma cells and CD4+/CD8+ T cells.

Obliterative Endarteritis: Cell proliferation and infiltration around the vessels damage the intima and narrow or close small arteries (endarteritis obliterans). This is what causes central necrosis in the primary chancre and the extensive tissue-destroying gummas of tertiary syphilis.

Clinical Features by Stage

Primary Syphilis:

• Chancre: appears after an incubation period of 10–90 days (3 weeks on average) where the bacteria entered (glans penis, vulva, anus, lips or tongue).
• Features: a single round or oval ulcer 1–2 cm across with a clean base that feels firm like cartilage (indurated base); it is painless and does not itch. The ulcer heals by itself within 3–6 weeks even without treatment.
• Regional lymph nodes: enlarged, firm, painless, non-suppurating inguinal nodes on both sides.

Secondary Syphilis:

• Develops 2–8 weeks after the chancre disappears and reflects spread of the bacteria through the bloodstream.
• Syphilitic roseola: pale pink macules on the flanks, abdomen and chest that do not itch and blanch under glass pressure.
• Palmar and plantar syphilides: well-defined, copper-red to reddish-brown papules and macules ringed by a collar of scale (Biett's collarette).
• Condyloma lata: moist, flat-topped, grayish-white papules clustered in the anogenital folds, teeming with spirochetes.
• Syphilitic alopecia: patchy "moth-eaten" hair loss on the scalp, usually over the occipital and temporal areas.

Latent Syphilis: There are no signs on the skin or mucous membranes; the infection is detected only by positive blood tests. It is divided into early latent syphilis (<1 year) and late latent syphilis (>1 year).

Tertiary Syphilis:

• Gumma: a mass in the skin, bone or internal organs that gradually necroses in the center and breaks down into a deep ulcer with a dirty base, healing with a puckered scar.
• Cardiovascular syphilis and neurosyphilis: aortic aneurysm, tabes dorsalis, Argyll Robertson pupils (loss of the light reflex with preserved accommodation) and dementia.

How We Diagnose Syphilis at Haute-Derma

Darkfield Microscopy: Fluid from a primary chancre or condyloma lata is examined directly under a darkfield microscope, which shows corkscrew-shaped T. pallidum moving back and forth and rotating around their long axis.

Two-Step Serologic Testing (Reverse or Traditional Algorithm):

• Non-treponemal tests (RPR / VDRL): measure antibody titers (1:4, 1:16, 1:32 and so on). They are used to track disease activity and response to treatment; after treatment the RPR titer should fall at least fourfold (two dilutions).
• Treponemal tests (TPHA / TP-PA / FTA-ABS / rapid syphilis tests): specifically detect antibodies against T. pallidum. Once positive, they usually stay positive for life.

Palm Dermoscopy and Skin Biopsy:

• Dermoscopy of palm lesions shows the characteristic raised Biett's collarette at the edge around a copper-red center.
• Histology shows perivascular inflammation with a dense infiltrate of plasma cells.

Treatment and Follow-Up at Haute-Derma

Standard Antibiotic Regimens (CDC / WHO Guidelines)

• Primary, secondary and early latent syphilis (<1 year):
  • Benzathine penicillin G: a single deep intramuscular dose of 2.4 million units, split into two injections, one in each buttock.
  • Alternative for penicillin allergy: doxycycline 100 mg by mouth twice daily for 14 days.
• Late latent syphilis (>1 year) or tertiary syphilis:
  • Benzathine penicillin G: 2.4 million units intramuscularly once a week for 3 consecutive weeks (7.2 million units in total).
  • Alternative for penicillin allergy: doxycycline 100 mg by mouth twice daily for 28 days.

Managing the Jarisch-Herxheimer Reaction

• Occurs in 50–75% of patients with secondary syphilis within 2–24 hours of the first penicillin injection, as large numbers of dying spirochetes release lipoproteins.
• Symptoms: high fever, chills, headache, muscle aches and a temporary flare of the rash.
• Our approach: we warn patients in advance and, if needed, give paracetamol and a short course of oral corticosteroids.

Post-Treatment Monitoring and Cosmetic Recovery

• Regular RPR checks: RPR titers are measured 3, 6, 12 and 24 months after treatment. Treatment is considered successful when the titer falls at least fourfold (for example, from 1:32 to 1:8 or lower).
• Scars and pigmentation: once the infection has been cleared, a 1064 nm Nd:YAG laser can fade residual red-brown marks on the palms, and fractional CO2 laser can remodel scars left by gummas.