Pediatric case of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis with immunoglobulin a deposition diagnosed early through school urinary screening.

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a rare but severe condition in children, and renal involvement in the form of ANCA-associated glomerulonephritis (AAGN) usually determines prognosis. Although AAGN is characterized by pauci-immune necrotizing crescentic glomerulonephritis, mesangial immunoglobulin A (IgA) deposition occurs in a subset of patients; however, pediatric cases remain exceptionally rare. We aimed to report a case of a 12-year-old girl who was asymptomatic and diagnosed through routine school urinalysis. She presented with hematuria and progressive proteinuria, accompanied by elevated myeloperoxidase (MPO)-ANCA levels, while renal function was preserved. Renal biopsy revealed a cellular crescent with surrounding inflammatory cell infiltration, consistent with AAGN. Immunofluorescence microscopy demonstrated mesangial deposition of IgA, immunoglobulin M, and C3; however, there was no mesangial cell proliferation or matrix expansion to suggest typical IgA nephropathy. Based on the clinical course and pathological findings, the primary pathological process was considered to be AAGN rather than IgA nephropathy. The patient was treated with methylprednisolone pulse therapy, followed by rituximab and maintenance therapy with azathioprine. MPO-ANCA levels and proteinuria normalized, and no relapse has been observed. This case highlights the significance of early detection of pediatric renal-limited AAV and suggests that timely AAV-based immunosuppressive therapy promotes favorable outcomes in pediatric AAGN with IgA deposition.