Maternal Sjögren's Disease and Its Long Shadow: Adult-Onset Seronegative Lupus Nephritis Following Congenital Heart Block.

Congenital complete atrioventricular block (CCAVB) is a well-recognized manifestation of neonatal lupus erythematosus (NLE), caused by transplacental transfer of maternal anti-Ro/Sjögren's Syndrome Type A (SSA) and anti-La/Sjögren's Syndrome Type B (SSB) antibodies. Although non-cardiac manifestations of NLE typically resolve within the first year of life, the long-term autoimmune risk in affected offspring remains unclear. We report a 24-year-old woman with CCAVB secondary to maternal Sjögren's disease who presented with acute heart failure, nephrotic-range proteinuria, bicytopenia, pericardial effusion, and findings concerning for Libman-Sacks endocarditis. Despite negative conventional lupus serologies, renal biopsy demonstrated Class IV/V lupus-like immune-complex glomerulonephritis with full-house immune complex deposition, leading the multidisciplinary team to favor seronegative lupus nephritis. This case demonstrates the diagnostic limitations of serology-based approaches in atypical lupus presentations and underscores the critical role of tissue biopsy. The case also raises questions regarding long-term autoimmune risk after autoimmune congenital heart block, an area for which prospective data and evidence-based surveillance strategies remain limited.