Abstract: SA-PO0785
C3 Glomerulonephritis Mimicking ANCA-Associated Vasculitis in the Setting of Monoclonal Gammopathy
Session Information
- Glomerular Diseases: Lupus Nephritis, Monoclonal Gammopathy-Related Disease, and Transplantation
October 24, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Glomerular Diseases
- 1402 Glomerular Diseases: Clinical, Outcomes, and Therapeutics
Authors
- Lledo, Anthony L., Novant Health New Hanover Regional Medical Center, Wilmington, North Carolina, United States
- Havill, John, Eastern Nephrology Associates PLLC, Wilmington, North Carolina, United States
- Wang, Bangchen, Duke University School of Medicine, Durham, North Carolina, United States
Introduction
C3 glomerulonephritis (C3GN) is a rare complement mediated glomerular disease caused by dysregulation of the alternative complement pathway. In older adults, C3GN has been increasingly associated with monoclonal gammopathy (MG). Crescentic C3GN may closely mimic ANCA-associated vasculitis, creating significant diagnostic and therapeutic challenges.
Case Description
A 66 y/o male with T2DM presented with 3 weeks of progressive bilateral lower extremity edema and severe AKI requiring hemodialysis. His course was complicated by left lower extremity cellulitis and a vasculitic rash. Initial evaluation showed nephritic syndrome with active urinary sediment, subnephrotic proteinuria, and low C3 levels. ANCA-associated vasculitis was initially suspected.
Kidney biopsy demonstrated crescentic glomerulonephritis with dominant C3 staining. Electron microscopy revealed subepithelial, intramembranous, and mesangial electron dense deposits. Serum studies identified biclonal IgG lambda and IgA lambda monoclonal proteins. ANCA serologies and infectious workup were negative.
Bone marrow biopsy and molecular studies were negative for a clonal plasma cell or lymphoproliferative disorder.
The patient was treated with pulse dose corticosteroids followed by mycophenolate mofetil. He remains dialysis dependent with improving renal function and urine output to date.
Discussion
This case highlights crescentic C3GN mimicking ANCA-associated vasculitis. Although crescent formation initially suggested a pauci-immune process, dominant C3 staining, low C3 levels, electron dense deposits, negative ANCA testing, and negative infectious studies supported complement mediated glomerular disease.
The presence of biclonal monoclonal proteins raised concern for MG-associated C3GN despite negative bone marrow findings. Small plasma cell clones may evade detection while producing nephrotoxic monoclonal immunoglobulins capable of dysregulating the alternative complement pathway. Clone directed therapy may improve renal outcomes.
Acknowledgment
We thank Dr. Laura Barisoni, Duke Department of Pathology, Duke University SOM, for assistance with case coordination.
(A) LM showing a cellular crescent within a glomerulus. (B) IF demonstrating dominant mesangial and capillary wall C3 staining. (C) EM showing subepithelial, intramembranous, and mesangial electron dense deposits.