Pediatric Proliferative Glomerulonephritis with Unique IgG4

Introduction: Proliferative Glomerulonephritis with monoclonal IgG deposits (PGNMID) is a recently established diagnosis defined by monoclonal immunoglobulin deposition in the glomerulus. PGNMID is rare and typically found in the adult population. Here, we present a unique case of pediatric PGNMID secondary to IgG4 deposition. Case Description: A 10-year-old female with history of metastatic neuroblastoma status post extensive chemotherapy and abdominal radiation in remission on long-term difluoromethylornithine developed hematuria, proteinuria (protein:creatinine ratio 14), glycosuria, and hypertension. She was determined to have stage 3a chronic kidney disease and was started on amlodipine. While awaiting renal biopsy she developed hypoalbuminemia, edema, and acute kidney injury requiring admission for augmented diuresis. Biopsy showed proliferative glomerulonephritis with IgG4 and kappa immunoglobulin deposits with moderate glomerular scarring and 15% interstitial fibrosis and tubular atrophy. Bone marrow biopsy was negative for clonal disorder. Serum protein electrophoresis was nondiagnostic due to oligoclonal bands from recent IVIG infusion. Urine Bence-Jones screen showed lambda light chain M-protein, an unexpected finding as the biopsy showed kappa. For her PGNMID versus IgG4-related disease, the patient was recently started on steroids and rituximab. Discussion: PGNMID is a recently described diagnosis, more commonly seen in adults, which can be a source of progressive kidney disease in children. PGNMID is most often caused by IgG3 and can be a monoclonal gammopathy of renal significance. In this case, PGNMID would not explain glycosuria which, along with IgG4 restriction and the light chain mismatch, leads to diagnostic uncertainty. Her disease may instead represent an overlap with IgG4 disease. Our goal in sharing this case is to raise awareness for both PGNMID and IgG4 disease in pediatric patients and emphasize the potential overlap in pathophysiology.