A pediatric case of C3 glomerulonephritis initially misclassified as IgA nephropathy with a favorable response to C3-targeted therapy.
Laura F Alconcher, Analía Sánchez Lucero, Celia Dos Santos et al.
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Case in brief
A previously healthy 13-year-old girl presented with nephrotic and nephritic syndrome and low serum C3. Her first biopsy showed mesangioproliferative glomerulonephritis with dominant IgA deposits, leading to an initial diagnosis of IgA nephropathy. Prednisone, mycophenolic acid and an angiotensin-converting enzyme inhibitor produced only partial remission, followed by relapse with persistent C3 consumption and C5b9 activation. A repeat biopsy established C3 glomerulonephritis (C3GN) with a membranoproliferative pattern. After prolonged lack of response to immunosuppression, pegcetacoplan was started; within 3 months, proteinuria and complement activation markers normalized.
What made this case unusual
The initial biopsy’s dominant IgA deposits obscured C3GN, and the diagnosis became clear only on repeat biopsy in the setting of treatment-refractory disease and persistent complement dysregulation.
Diagnostic / clinical pearl
In refractory glomerulonephritis with ongoing complement dysregulation, an initial biopsy suggesting IgA nephropathy may not settle the diagnosis; repeat biopsy can reveal C3GN.
Why it matters
The reported rapid remission after pegcetacoplan provides a case-level example of response to C3-targeted therapy in C3GN, without establishing efficacy beyond this patient.