Congenital syphilis refers to fetal infection caused by Treponema pallidum transmitted from the mother to the fetus through the placenta. During early pregnancy, the chorionic Langerhans cell layer serves as a barrier, making it difficult for the spirochete to reach the fetus. After the fourth month of pregnancy, the Langerhans cell layer undergoes degeneration and atrophy, allowing the spirochete to cross the placenta and enter the fetal circulation through the umbilical vein. As a result, most instances of placental transmission occur after the fourth month of gestation. Fetal infection depends on the stage of syphilis in the mother and whether appropriate treatment is administered during pregnancy. In cases of untreated primary or secondary maternal infection, almost all fetuses are affected. Among these, 50% experience miscarriage, preterm birth, stillbirth, or neonatal death. Surviving infants develop clinical symptoms at different ages after birth, with those under two years categorized as early congenital syphilis and those over two years falling into the category of late congenital syphilis. Early manifestations result mainly from active infection and inflammation, while late manifestations represent residual deformities or chronic damage from the early infection.
Clinical Manifestations
Most affected neonates are asymptomatic at birth, but symptoms gradually develop after 2–3 weeks. Early congenital syphilis is more common in preterm infants, low-birth-weight infants, or small-for-gestational-age infants. Affected neonates often exhibit delayed growth, development, and nutritional status compared to their gestational age. Common signs and symptoms include:
Skin and Mucosal Lesions
These occur in approximately 30–60% of cases. Rhinitis (commonly referred to as "snuffles") is an early feature, typically appearing in the first week after birth and persisting for up to three months. Symptoms include nasal congestion with initially clear, then purulent or bloody secretions, which contain high concentrations of the pathogen and are highly contagious. Nasal mucosal ulceration can involve the nasal cartilage, resulting in a "saddle nose" deformity, and laryngeal involvement can cause hoarseness. Skin rashes often develop 2–3 weeks after birth, initially presenting as pink or red polymorphic maculopapular lesions that later become brownish with fine scaling. Syphilitic pemphigus may also occur on the palms and soles. Distribution patterns, rather than morphology, are more characteristic and often involve the perioral, nasal, and perianal regions. The lesions may fissure radially after a few months.
Bone Lesions
Bone involvement is observed in 20–95% of cases, although it is often subclinical. Severe cases can result in "pseudoparalysis" due to intense pain. Long bones are commonly affected with symmetric, multifocal lesions visible on X-rays, showing features of osteochondritis and periostitis.
Generalized Lymphadenopathy
This occurs in approximately 20% of cases and is nontender, with enlargement of the epitrochlear lymph nodes being particularly notable for diagnostic purposes.
Hepatomegaly and Splenomegaly
Nearly all affected infants have hepatomegaly, with one-third also exhibiting syphilitic hepatitis characterized by jaundice and impaired liver function, which may persist for several months to half a year.
Hematologic Abnormalities
Findings include anemia, leukopenia or leukocytosis, thrombocytopenia, and Coombs-negative hemolytic anemia.
Central Nervous System (CNS) Symptoms
CNS involvement is rare in the neonatal period; symptoms often develop between 3–6 months of age, with meningitis being a common manifestation. Cerebrospinal fluid (CSF) typically shows elevated lymphocyte counts, moderate protein elevation, and normal glucose levels.
Other Symptoms
These include pneumonia, nephritis, chorioretinitis, and myocarditis. Late congenital syphilis manifests after the second year of life with features such as Hutchinson's teeth, saddle nose deformity, interstitial keratitis, sensorineural hearing loss, and developmental delays.
Diagnosis
Diagnosis primarily relies on maternal history, clinical features, and laboratory investigations. Diagnostic confirmation can be supported by:
- Examining placental, amniotic fluid, or lesion specimens for T. pallidum under a dark-field microscope, though detection rates are low.
- The Venereal Disease Research Laboratory (VDRL) test, which is simple, rapid, and highly sensitive, though false positives may occur. It is suitable as a screening test.
- The Rapid Plasma Reagin (RPR) test, which is widely used for syphilis screening, diagnosis, and monitoring. It is simple and rapid, with high sensitivity, and becomes positive within four weeks of infection. However, false negatives may occur, and confirmatory tests are needed.
- The Fluorescent Treponemal Antibody-Absorption (FTA-ABS) test, which is highly specific and sensitive, and frequently used for diagnostic confirmation.
- The Treponema Pallidum Particle Agglutination (TPPA) test, which is highly specific and can confirm the diagnosis. However, it does not revert to negative, making it unsuitable for evaluating treatment efficacy.
Treatment and Prevention
Penicillin is the first-line treatment, administered intravenously at a dose of 50,000 U/kg every 12 hours for the first 7 days, and then every 8 hours for a total of 10–14 days. In cases of penicillin allergy, erythromycin can be used at a daily dose of 15 mg/kg for 12–15 days, administered orally or via injection. Following treatment, RPR testing should be conducted at 3-month intervals (at 3, 6, 9, 12, 15, and 18 months) to monitor antibody titers until they decline or become negative. Proper and timely treatment of maternal syphilis during pregnancy is the most effective measure for reducing the incidence of congenital syphilis.