Congenital syphilis in a 4-month-old infant with limb weakness

Background

Each year, syphilis complicates more than 2 million pregnancies worldwide and continues to rise.¹ It is a preventable disease, and its existence in the 21st century in developed countries highlights failures in syphilis screening programmes and delivery of appropriate prenatal care.1 Whilst still uncommon, rates of congenital syphilis have been rising in developed countries over recent years.2 In 2018 alone, 1306 cases were reported in the USA, constituting a 185% increase since 2014.3

Congenital syphilis carries a considerable mortality of 10% and significant morbidity.2 The risk of vertical transmission is directly correlated with the stage of maternal syphilis during pregnancy.2 Cases of this disease can lead to perinatal/neonatal death, prematurity and low birth weight.2 Untreated, spontaneous abortion can occur in 40% of cases.2 Affected individuals often suffer long-term sequelae such as visual loss, sensorineural hearing loss, bone/joint deformity and neurodevelopmental delay.4 It is important to note that up to two-thirds of the affected infants may be asymptomatic at birth, and in certain cases, infection may persist for life.4

Thus, despite maternal screening and the existence of a readily available, inexpensive treatment, congenital syphilis remains a serious threat to global public health. This threat may be rare, but the rise in cases warrants concern and highlights the need for increased vigilance among clinicians.

This report describes a case of congenital syphilis diagnosed in a 4-month-old infant after presentation with a rash and reduced movement of left-sided limbs.

Case presentation

A 4-month-old girl presented to the Paediatric Assessment Unit at the Royal Bolton Hospital with a 3-month history of reduced movement of the left arm and leg alongside a blanching rash to both upper and lower limbs. The child was otherwise systemically well and reaching all other developmental milestones.

She was born via normal vaginal delivery in hospital at 40 weeks’ gestation. There was some possible intrauterine growth restriction noted on the 20-week ultrasound, but this had resolved by 35 weeks. The obstetric history of the mother was otherwise uneventful. All immunisations were up to date. Our patient had one maternal half sibling, aged 3 who was fit and well.

The parents were separated. The mother had a history of anxiety and postnatal depression and had a named social worker for previous domestic abuse. The father had likely juvenile idiopathic arthritis (JIA) at age 13/14, and no other relevant family history was reported.

The mother provided a history of an episode of unprotected sexual intercourse early in pregnancy, which took place after her first prenatal screening. She made multiple visits to her general practitioner (GP) during the pregnancy for joint/muscle aches, blurring of vision, hair loss and a rash she described as similar to her daughter’s. The mother states these were all treated as symptoms of pregnancy. She could not recall any primary chancre or ulcer in the genital region.

On examination, vital signs were normal. The infant was generally pale with a dusky pink blanching rash of 2–3 mm macules to both arms and legs (see figures 1 and 2). There were also papules to the palms and soles of feet with evidence of desquamation (see figures 3 and 4). Reduced power was found in the left-sided limbs, more prominent in the arm with movement only against gravity and no grasp reflex. There was no obvious pain or swelling to the limbs. Possible hepatomegaly was felt on abdominal examination. Examination of all other systems was unremarkable. Head circumference was 41 cm (75th to 91st centile) and weight 5.2 kg (75th to 91st centile).

Investigations

Initial blood results are shown in table 1; of note, they show raised inflammatory markers (C reactive protein and erythrocyte sedimenation rate) with a slight microcytic anaemia, raised alkaline phosphatase and suppressed thyroid stimulating hormone. Results of a capillary blood gas were normal.

An X-ray of the affected limb can be found in figure 5 and shows periosteal inflammation mainly to the left ulna, but abnormalities are also present in the distal humerus and proximal radius.

Results of further tests included a negative screen for toxoplasmosis, rubella, cytomegalovirus, HIV and herpes simplex, and negative peripheral blood cultures and connective tissue disease screen. Hepatitis B surface antigen was detected but thought to be due to recent immunisation. Of note, the maternal early pregnancy screen for HIV, hepatitis B and syphilis was also negative.

The patient was transferred to a tertiary centre for further investigations and specialist input. Full-body MRI showed high signal in the left radius and ulna, but no lesions or fractures were identified. No organomegaly was seen on imaging.

Following transfer, a congenital infection screen was repeated—this time including an anti-treponemal IgM enzyme immunoassay that returned as positive. A diagnosis of congenital syphilis was made. Cerebrospinal fluid (CSF) examination was normal with negative CSF treponemal testing. Ophthalmic examination showed no abnormalities.

Differential diagnosis

Initially, non-accidental injury was a considered diagnosis, given risk factors in the social history. However, the combination of clinical and serological abnormalities made such a diagnosis more unlikely. The X-ray findings then effectively ruled this diagnosis out.

Another differential included autoimmune conditions (such as neonatal lupus), given the rash, limb abnormalities, possible hepatomegaly and possible history of JIA in the father. Many autoimmune diseases can present in a similar manner with a constellation of non-specific symptoms and therefore often pose diagnostic difficulty.

Congenital infection was also suspected, given the raised inflammatory markers in conjunction with the clinical findings. As with autoimmune conditions, congenital infection can often present with myriad symptoms and thus was also an important consideration here.

Treatment

Following the detection of treponemal IgM, the patient was commenced on a 10-day course of intravenous benzylpenicillin. She also received input from the physiotherapy team to assist with limb mobility.

Both parents were advised to attend the genitourinary medicine clinic. The mother also tested positive for anti-treponemal IgM and was treated and followed up accordingly with the sexual health team.

Outcome and follow-up

The child was discharged with outpatient infectious diseases and general paediatric follow-up at 3, 6 and 12 months, as per the most recent national guidelines for management of syphilis, from 2015.5 These guidelines recommend clinical and serological follow-up with repeat quantitative non-treponemal testing, such as rapid plasma reagin (RPR) titres, until negative.5 At 6 months after discharge, RPR titre for this patient was 1:12, and at 12 months it was negative, showing an adequate response to treatment.

At 12-month follow-up, the child has no residual weakness and is now meeting all developmental milestones. Audiological screening has also found no abnormalities.