neonatal lupus

Neonatal lupus results from passive transfer of maternal IgG autoantibodies (primarily anti-Ro/SSA, less commonly anti-La/SSB, rarely anti-U1-RNP) across the placenta starting around 12-16 weeks gestation. These antibodies bind fetal cardiac conduction tissue (particularly the AV node) and skin, triggering an inflammatory and fibrotic response. Mothers may be asymptomatic carriers of these antibodies or have overt Sjögren syndrome or SLE; many are diagnosed only after the infant is affected.

Clinical manifestations: 1. Cutaneous: Annular, erythematous, scaly plaques typically on the face (periorbital 'raccoon eyes' pattern) and scalp, often appearing after UV exposure in the first weeks of life. Resolves spontaneously by 6-12 months as maternal antibodies are cleared, usually without scarring (may leave telangiectasias or dyspigmentation). 2. Cardiac: Congenital complete (third-degree) heart block is the most serious and irreversible manifestation, caused by antibody-mediated fibrosis of the AV node, usually detected in utero (bradycardia) between 18-24 weeks gestation. May require fetal/neonatal pacemaker placement; carries significant morbidity/mortality. 3. Hepatobiliary: Transient transaminitis, cholestasis, or hepatosplenomegaly. 4. Hematologic: Thrombocytopenia, neutropenia, or anemia, typically transient.

Diagnosis involves detecting maternal and infant anti-Ro/La antibodies, EKG/echocardiogram for heart block, and skin biopsy if needed (interface dermatitis). Screening at-risk pregnancies (mothers with known anti-Ro/La antibodies) with serial fetal echocardiography is recommended, especially in mothers who have had one affected child (recurrence risk ~15-20%).

Management: Pacemaker for complete heart block; sun protection and topical steroids for skin lesions; monitoring for resolution of hematologic/hepatic abnormalities. Hydroxychloroquine during pregnancy may reduce recurrence risk of cardiac NLE in subsequent pregnancies.

Key distinction from SLE: NLE is a passively acquired antibody-mediated disease, not a primary autoimmune disease of the infant; it resolves as maternal antibodies degrade except for the heart block, which is due to permanent fibrotic damage to conduction tissue.