IgA-dominant postinfectious glomerulonephritis: a new twist on an old disease.

IgA-dominant acute postinfectious glomerulonephritis (APIGN) is an increasingly recognized morphologic variant of APIGN, particularly in the elderly. In contrast to classic APIGN, in which there is typically glomerular deposition of IgG and C3 or C3 only, IgA is the sole or dominant immunoglobulin in IgA-dominant APIGN. Because the vast majority of reported cases occur in association with staphylococcal infections, the alternative designation 'IgA-dominant acute poststaphylococcal glomerulonephritis' has been applied. Diabetes is a major risk factor, likely reflecting the high prevalence of staphylococcal infection in diabetics, particularly involving skin. Patients typically present with severe renal failure, proteinuria and hematuria. Prognosis is guarded with less than a fifth of patients fully recovering renal function. This variant of APIGN must be distinguished from IgA nephropathy. Features that favor IgA-dominant APIGN over IgA nephropathy include initial presentation in older age or in a diabetic patient, acute renal failure, intercurrent culture-documented staphylococcal infection, hypocomplementemia, diffuse glomerular endocapillary hypercellularity with prominent neutrophil infiltration on light microscopy, stronger immunofluorescence staining for C3 than IgA, and the presence of subepithelial humps on electron microscopy. The pathogenetic mechanism of selective IgA deposition in patients with poststaphylococcal glomerulonephritis likely involves specific host responses to the inciting pathogen.