Abstract: SA-PO0716
The Wolf in C3's Clothing: Unmasking Subacute Endocarditis in a C3 Glomerulopathy Masquerade
Session Information
- Glomerular Diseases: Complement-Mediated Glomerulopathies and Infection-Related GN
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
- Bartholow, Samantha Jane, Rush University Medical Center, Chicago, Illinois, United States
- Baxi, Pravir V., Rush University Medical Center, Chicago, Illinois, United States
Introduction
Subacute infective endocarditis (IE) poses a diagnostic challenge due to its insidious onset, often presenting with months of non-specific symptoms rather than classic stigmata. When complicated by infection-related glomerulonephritis (IRGN), kidney biopsy findings can mimic C3 glomerulopathy (C3GN) via dominant C3 staining and minimal immunoglobulin (Ig) deposition. Failure to recognize this histopathologic red herring can lead to the start of immunosuppression (IS) and the delay of necessary antibiotics (Abx).
Case Description
A 63-year-old man with a bioprosthetic aortic valve presented with a 2-week onset of petechial rash and 4 months of fatigue and malaise following an URI. Symptoms persisted despite outpatient Abx. His wife noted a 40-lb weight loss and slow functional decline. He was afebrile and non-toxic on exam. His labs: WBC 11, Hgb 9, plts 71, creatinine (Cr) 1.65 mg/dL (baseline 1.0). UA showed dipstick protein and blood; 127 RBCs, UACR 1.6 g/g, and UPC 2.9 g/g. Serologies were notable for low C3 (65) and C4 (11). TTE was negative for vegetations. A bone marrow biopsy for bicytopenia was non-diagnostic. With his rising Cr and concern for RPGN, steroids were started and a kidney biopsy was done. He subsequently decompensated and was transferred to the ICU while pending results. Biopsy (Fig 1) revealed proliferative and focally necrotizing GN with dominant C3 staining (negative IgG/IgA) - a pattern most consistent with C3GN. Given his clinical history, additional ID and cardiac workup was pursued; Streptococcus sanguinis bacteremia and new valvular decline confirmed the clinical diagnosis of IE. Ceftriaxone was initiated and his clinical status improved over the next 5 days.
Discussion
This case highlights the diagnostic pitfall of IE-associated GN presenting with a C3-dominant rather than classic IRGN pattern. Dominant C3 staining with minimal Ig deposition may be misread as primary C3GN—prompting dangerous IS use while delaying Abx. Clinicians should maintain a high index of suspicion for IRGN in patients with AKI, hypocomplementemia, and IE risk factors. TEE and utilizing pronase digestion to unmask hidden Ig should also be considered to prevent misdiagnosis.
Acknowledgment
Google Gemini used for spelling/grammar but not content.
Left: H&E stain
Right: C3 IF