Neonatal lupus erythematosus — SCE Dermatology MCQ

Correct answer: D — Transplacental anti-Ro or anti-La antibodies

The correct answer is D, transplacental anti-Ro or anti-La antibodies, which cause neonatal lupus erythematosus (NLE). Maternal IgG antibodies against Ro/SSA and La/SSB cross the placenta and cause inflammatory damage to fetal skin (producing photosensitive, annular, periorbital and scalp plaques after UV exposure) and to the fetal cardiac conducting system, causing fibrosis of the AV node and congenital heart block, classically first degree progressing to complete block. The maternal history of photosensitive arthralgia points to underlying maternal Sjogren syndrome or SLE, the conditions most associated with these autoantibodies, even if the mother herself is undiagnosed or minimally symptomatic. This triad of neonatal photosensitive rash, cardiac conduction disease and a mother with autoimmune features is pathognomonic for anti-Ro/La mediated neonatal lupus and mandates maternal autoantibody testing and infant ECG monitoring. Why the other options are wrong: E. Congenital parvovirus B19 infection: causes fetal anaemia, hydrops and myocarditis, not a photosensitive annular rash or isolated heart block, and does not explain the maternal photosensitive arthralgia. C. Keratin 1 mutation in the epidermis: causes epidermolytic ichthyosis with blistering and hyperkeratosis from birth, unrelated to photosensitivity, cardiac conduction defects or maternal symptoms. B. IgE-mediated cow's milk allergy: presents with urticaria, angioedema or gastrointestinal symptoms after feeding, not annular photosensitive plaques or heart block. A. Postnatal infection with herpes simplex virus: produces vesicular or ulcerative lesions with systemic sepsis-like illness, not annular photosensitive plaques, and has no link to maternal arthralgia or fetal conduction disease. Key point: Photosensitive annular rash plus congenital heart block in a neonate, with a mother who has autoimmune features, is neonatal lupus from transplacental anti-Ro/anti-La antibodies until proven otherwise.

Reference: NHS Greater Glasgow and Clyde Paediatric Guidelines (Right Decisions Scotland): Guideline for the management of babies born to mothers with SLE and other autoimmune disorders, anti-Ro/anti-La antibodies, https://clinicalguidelines.scot.nhs.uk/ggc-paediatric-guidelines/ggc-paediatric-guidelines/neonatology/anti-ro-anti-la-antibodies-guideline-for-the-management-of-babies-born-to-mothers-with-systemic-lupus-erythematosus-sle-and-other-autoimmune-disorders/