Poststreptococcal acute glomerulonephritis superimposed on chronic kidney disease due to dysplastic kidney in an...

We report an 11-year-old boy with chronic kidney disease (CKD) stage 3 due to right multicystic dysplastic kidney and contralateral dysplasia who developed poststreptococcal acute glomerulonephritis (PSAGN) that rapidly progressed to kidney failure despite intensive immunosuppressive treatment. He presented with oliguria, macrohematuria, heavy proteinuria, hypocomplementemia, and an elevated antistreptolysin O titer. Initial kidney biopsy revealed diffuse endocapillary proliferation with prominent C3 deposition, subepithelial humps, and positive staining for nephritis-associated plasmin receptor (NAPlr), consistent with PSAGN. Kidney dysfunction persisted despite the administration of methylprednisolone pulse therapy, prednisolone, cyclosporine, and mycophenolate mofetil. A second biopsy at 4 months revealed focal segmental glomerulosclerosis, diffuse foot process effacement, and negative staining for NAPlr, suggesting transition from a glomerular inflammatory process to a hyperfiltration-driven structural injury. Comprehensive genetic analysis did not identify any pathogenic variants associated with bilateral dysplastic kidney. Peritoneal dialysis was initiated on day 182, and living donor kidney transplantation was performed 10 months after nephritis onset, with favorable early outcomes. This case highlights that PSAGN superimposed on CKD with reduced nephron mass may result in rapid kidney function deterioration despite aggressive treatment.