Diagnostic dilemmas in a girl with acute glomerulonephritis: Answers

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Based on the initial presentation of macroscopic hematuria, proteinuria, and renal failure following an episode of pharyngitis with a typical time lag of 2 weeks, the differential diagnosis consists primarily of acute post-infectious glomerulonephritis (PIGN), the first presentation of either immune complex, or complement-mediated mem branoproliferative nephritis (MPGN), or IgA nephropathy (IgAN) triggered by an infection. Less likely, but not excluded, are ANCA vasculitis, lupus nephritis, antiglomerular basement (GBM) glomerulonephritis, and toxicity-/medication-induced glomerulonephritis. The young age and lack of sinusitis or pulmonary symptoms make ANCA vasculitis less likely and there were neither physical nor anamnestic signs of systemic lupus erythematosus (SLE). Macroscopic hematuria and nephrotic proteinuria are less consistent with a toxic cause of acute kidney injury. Given the clinical course, the patient had suspected rapidly progressive glomerulonephritis (RPGN). 2. Additional laboratory investigations should be aimed at possible causes of RPGN [1]. The few available studies on pediatric RPGN report that it is caused in over 80% by a form of immune-complex-mediated glomerulonephritis, with MPGN, Henoch–Schönlein purpura (HSP)/IgA nephropathy and PIGN as the most frequent underlying causes [2–5]. Lupus nephritis, C3 glomerulonephritis (C3GN), and ANCA vasculitis are more infrequent causes of pediatric RPGN [2–5]. In our patient, additional serummeasurements included anti-streptolysin titer (AST) and anti-DNAse B titer, mycoplasma, hepatitis B andC serology, ANA, anti-PR3 ANCA, anti-MPO ANCA, anti-GBM measurements, and a full complement cascade for assessment of both the classical and alternative pathways (C3, C4, C3d, AP50, CH50, C3 nephritic factor, C5b-9). 3. On the day after admission, the patient developed oliguria and a steep rise in creatinine level, indicating a rapid progression of renal failure. Although therewas a high degree of suspicion regarding PIGN, serum complement C3 and C4 levels and AST and anti-DNAse B titer were not yet available. Generally, a renal biopsy is not mandatory when PIGN is suspected. However, certain features atypical of PIGN should prompt a biopsy. These include RPGN, extra-renal This refers to the article that can be found at doi: 10.1007/s00467-0173625-4