Dermatology MCQ - Inflammatory Dermatoses - Neonatal lupus erythematosus

A 3-week-old infant is brought to the clinic for a well-baby visit. The mother has a history of Sjögren's syndrome but is currently asymptomatic. On examination, the infant has prominent, annular, erythematous plaques with a slight scale and central clearing on the scalp and periorbital area. Which of the following is the most critical investigation to perform in this infant?

A. Skin biopsy for direct immunofluorescence
B. Serologic testing for anti-Ro/SSA and anti-La/SSB antibodies in the infant
C. A 12-lead electrocardiogram
D. Patch testing to rule out a contact allergen
E. Liver function tests

Correct Answer: C. A 12-lead electrocardiogram

Explanation

Neonatal lupus erythematosus (NLE) is a passive autoimmune condition caused by the transplacental passage of maternal autoantibodies, most commonly anti-Ro/SSA and anti-La/SSB. The clinical presentation is variable, but the most characteristic manifestations are cutaneous lesions and congenital heart block.

• Most Critical Investigation: While the skin rash is the most common finding, the most serious and potentially life-threatening complication of NLE is congenital complete heart block, which can be irreversible and may require a pacemaker. Therefore, in any infant with suspected NLE (based on the classic rash and/or maternal antibody status), the most urgent and critical investigation is a 12-lead ECG to assess cardiac conduction. The rash of NLE is transient and resolves as maternal antibodies are cleared, but the heart block is permanent.

Why other options are incorrect

• A. Skin biopsy for direct immunofluorescence: A biopsy may show histologic features suggestive of lupus, but it is not the most critical test. The diagnosis is primarily clinical and serological. Direct immunofluorescence is not routinely necessary.

• B. Serologic testing for anti-Ro/SSA and anti-La/SSB antibodies in the infant: This will almost certainly be positive, as it confirms the exposure to the pathogenic antibodies. However, it is not as critical as the ECG, as the management of a positive antibody test is to look for complications (like heart block), not to treat the antibody level itself. This test is important for confirmation but does not take precedence over ruling out a life-threatening condition.

• D. Patch testing to rule out a contact allergen: The annular, photodistributed plaques are not typical for a contact allergen. The clinical picture and maternal history are highly specific for NLE.

• E. Liver function tests: Hepatic involvement (elevated transaminases) and cytopenias can occur in NLE, but they are less common and generally less urgent than the risk of complete heart block.

Key Associations for Neonatal Lupus Erythematosus (NLE)

• Pathogenesis: NLE is a model of passively acquired autoimmunity. IgG autoantibodies (anti-Ro/SSA, anti-La/SSB, and less commonly anti-U1-RNP) cross the placenta and cause tissue injury in the fetus and neonate. The mother may have SLE, Sjögren's syndrome, or be entirely asymptomatic.

• Clinical Features:

  • Cutaneous: The classic rash consists of annular or polycyclic, erythematous plaques, often in a periorbital "owl-eye" or "raccoon-eye" distribution. The lesions are frequently photosensitive and appear in the first few weeks of life.

  • Cardiac: Congenital complete heart block is the most serious manifestation. It typically develops in utero, often between 18-24 weeks of gestation, and is irreversible.

  • Other: Hepatic involvement (cholestasis, elevated LFTs), hematologic abnormalities (thrombocytopenia, anemia), and less commonly neurological symptoms.

• Diagnosis: Diagnosis is based on the characteristic clinical findings in the neonate and the demonstration of maternal (and hence neonatal) anti-Ro/SSA and/or anti-La/SSB antibodies.

• Differential Diagnosis: Includes tinea corporis, seborrheic dermatitis, atopic dermatitis, and other neonatal rashes. The distribution, appearance, and maternal history are key to differentiation.

• Management & Prognosis:

  • Cutaneous Disease: Is typically self-limited and resolves by 6-8 months of age as maternal antibodies are cleared. Management involves sun protection and possibly mild topical corticosteroids.

  • Cardiac Disease: Congenital heart block is permanent. Management involves close cardiology follow-up. Infants with a slow ventricular rate (<55 bpm) or signs of heart failure often require pacemaker implantation.

  • Prognosis: The prognosis for the rash and non-cardiac manifestations is excellent. The prognosis for cardiac involvement depends on the severity of the heart block and the associated cardiac complications. The mortality rate for infants with congenital heart block is significant, primarily due to hydrops fetalis or complications of pacing.