Fibrillary Glomerulonephritis or Complement 3 Glomerulopathy: A Rare Case of Crescentic Glomerulonephritis with C3 Dominant Glomerular Deposition and Positive DNAJB9

Introduction: Fibrillary glomerulonephritis (FGN) and complement 3 glomerulopathy (C3G) are two rare forms of GN. FGN is diagnosed by electron microscopy (EM) showing randomly oriented fibrils ranging in diameter from 15-25 nm. Immunofluorescence (IF) in FGN typically is IgG-predominant. C3G is diagnosed by isolated C3 (>3+ intensity) or dominant C3 (≥2 orders of intensity from other deposits) on IF. We present a rare case of crescentic GN with dominant C3 glomerular staining-consistent with C3G-but EM findings suggestive of FGN. Case Description: A 57-year-old female with history of HTN, type 2 DM, questionable SLE (not on therapy), presented with gross hematuria & lower extremity edema. BP 113/71, pulse 88. Creatinine 1.82mg/dL (0.75 two months prior). Urinalysis with 132RBC/hpf & 51WBC/hpf. Urine Prot/Cr 24. Cultures grew mixed flora in urine & Serratia marcescens in blood, treated with ceftriaxone. Other labs included serum albumin 1.8 g/dL, ANA >12.0, SS-A >8.0, C3 202, C4 57, & HbA1c 7.3%. Anti-dsDNA, hepatitis B & C, and HIV were negative. Kidney biopsy was performed. LM: diffuse necrotizing crescentic (15 of 15) GN, focal areas of double contours. IF: dominant 3+ C3 granular stain of capillary loops, lesser 1+ IgG. Remaining IF stains negative. Testing for alternative complement dysregulation was negative. EM showed fibrillary structures within basement membranes & mesangium (mean diameter 14 nm). DNAJB9 staining was positive. Patient was treated with steroids & cyclophosphamide but became dialysis dependent. Discussion: FGN is associated with autoimmune disease, dysproteinemia, hepatitis C, & malignancy. Our patient’s EM findings & positive DNAJB9 strongly support a diagnosis of FGN likely due to an autoimmune etiology given her prior history and positive ANA, SS-A. However, the patient’s IF findings of dominant C3 deposits is atypical for FGN, but rather characteristic of C3G which is caused by complement dysregulation. To the best of our knowledge, this is the first reported case of FGN to show dominant C3 glomerular deposits. Further studies are needed to determine the significance of this finding.