Intersecting Autoimmunities: ANCA and Anti-GBM Overlap in a Patient With Sjögren's Disease.

Background: The coexistence of antineutrophil cytoplasmic antibodies (ANCAs) and antiglomerular basement membrane (anti-GBM) antibodies defines a rare but clinically significant autoimmune overlap syndrome. This dual positivity can result in rapidly progressive glomerulonephritis, often with poor kidney outcomes. Diagnosis is particularly challenging in patients with underlying systemic autoimmune diseases, such as Sjögren's disease, where overlapping immunopathogenic mechanisms may obscure the clinical picture. Prompt recognition and individualized treatment are critical for optimal management. Case Presentation: We describe a 62-year-old woman with a history of primary Sjögren's disease who presented with acute kidney injury and urinary abnormalities. Serologic tests revealed high titers of myeloperoxidase (MPO)-ANCA and anti-GBM antibodies, as well as ANA and anti-Ro/La positivity. Kidney biopsy demonstrated crescentic glomerulonephritis with linear IgG deposition and significant chronic changes. Immunosuppressive therapy with high-dose corticosteroids was initiated; however, due to advanced fibrosis and glomerulosclerosis, further immunosuppression was not pursued. The patient required dialysis but remained clinically stable during follow-up. Conclusion: This case highlights the diagnostic and therapeutic challenges of dual ANCA and anti-GBM antibody positivity in the context of systemic autoimmunity. In patients with autoimmune disorders such as Sjögren's disease, a high index of suspicion is essential to detect this rare overlap, which often presents with severe kidney impairment. Although kidney prognosis is frequently poor, early identification and appropriate intervention are vital for improving clinical outcomes.