Infection-Related Glomerulonephritis Associated with Enterococcus faecium Pyelonephritis

Introduction: Infection-related glomerulonephritis (IRGN) is an immune-complex-mediated glomerular injury triggered by infections. A classic example is post-streptococcal glomerulonephritis (PSGN) in children. Other subtypes include IgA-dominant IRGN, endocarditis-associated GN, and shunt nephritis. It typically presents with hypocomplementemia and a diffuse exudative GN with C3-dominant or co-dominant depositions. We report a rare case of IRGN due to Enterococcus faecium pyelonephritis in an immunocompromised adult with chronic urinary tract instrumentation. Case Description: A 64-year-old woman with advanced recurrent high-grade serous endometrial cancer on trastuzumab and CKD stage IIIb due to obstructive uropathy and recurrent UTIs (managed with a suprapubic catheter and bilateral ureteral stents) presented with poor oral intake, nausea, diarrhea, catheter leakage, and lower extremity edema. She was afebrile, but her WBC was 14.5 × 10^9/L. Her creatinine rose from a baseline of 1.3 mg/dL to 5.91 mg/dL over 7 days. Urinalysis showed hematuria, proteinuria, pyuria, and bacteriuria. Initial cultures were mixed flora; one later grew Enterococcus faecium. Imaging was negative for obstruction. She was thought to have acute tubular necrosis. Renal biopsy revealed acute and chronic pyelonephritis with mesangial C3 deposition, favoring infection-related GN. There were no crescents, no endocapillary proliferation, and immunofluorescence showed 2+ mesangial C3 with the absence of immunoglobulins. Electron microscopy revealed mesangial electron-dense deposits and rare subepithelial humps. These findings, along with renal recovery on antibiotics alone, supported a diagnosis of C3-dominant IRGN. Discussion: Severe pyelonephritis with extensive renal parenchymal compromise is an unusual but documented cause of acute kidney injury. The co-existence of C3 deposition demonstrating additional injury through extensive alternative pathway activation is less well documented and should be considered in atypical presentations such as this case, in which renal recovery with antibiotics alone favored infection-driven injury over C3 glomerulopathy (C3G), which requires immunosuppression. This case emphasizes the importance of considering IRGN in patients with AKI, chronic UTIs, and atypical clinical features to avoid misdiagnosis and overtreatment.