Insidious Presentation of IgA Fibrillary Glomerulonephritis

Introduction: Fibrillary glomerulonephritis (FGN) is a rare diagnosis, present in 0.5 to 1.4% of native kidney biopsies. Symptoms include proteinuria, hematuria, kidney function impairment, hypertension (HTN), and monoclonal gammopathy. Positive DNAJB9 stain and large, non-branching overlapping fibrils on kidney biopsy confirm the diagnosis. We present a case of FGN in a patient with known chronic kidney disease (CKD). Case Description: An 80-year-old male with history of CKD stage 3b, HTN, benign prostatic hyperplasia, bladder calculi with obstructive uropathy status post transurethral resection of the prostate, atrial fibrillation on apixaban, and coronary artery disease presented for outpatient nephrology evaluation of elevated creatinine (Cr). He also had proteinuria and microscopic hematuria, ongoing for the past four years. Initially, hematuria was thought to be non-glomerular in nature due to prior urologic history. Patient also had new-onset bilateral lower extremity edema but denied urinary symptoms. His Cr was 1.7 mg/dL (eGFR 39 mL/min), compared to Cr 1.4mg/dL (eGFR 49 mL/min) eight months prior. Urinalysis showed proteinuria, hematuria, and red blood cell casts. Workup was significant for elevated free kappa and lambda light chains without apparent M-spike on protein electrophoresis; urine studies were positive for albumin and alpha-1, alpha-2, beta, and gamma globulins. CT abdomen/pelvis completed six months prior showed only small renal cysts; retroperitoneal ultrasound was significant for bilateral echogenic kidneys. Over the next five months, the patient continued to have lower extremity swelling; Cr at follow-up was 3.2mg/dL. He developed hypocalcemia and hyperphosphatemia. Urological evaluation for post-renal causes, including cystoscopy, was unrevealing. Kidney biopsy was significant for negative Congo red stain and positive DNAJB9 stain. Electron microscopy confirmed FGN, and immunofluorescence was significant for mesangial IgA, IgM, C3, kappa, and lambda staining. The patient was started on systemic steroids and rituximab treatment; he completed two doses of rituximab treatment with improvement in Cr. Discussion: Our patient had common manifestations of FGN years prior to initial nephrology evaluation, at which point his FGN rapidly progressed prior to rituximab treatment. This case highlights the importance of consideration and timely diagnosis of glomerulonephritis and emphasizes avoiding anchor bias.