IgA-dominant acute poststaphylococcal glomerulonephritis complicating diabetic nephropathy

Two pathological patterns of acute poststaphylococcal glomerulonephritis are well defined and include (1) an acute proliferative and exudative glomerulonephritis closely resembling classical acute poststreptococcal glomerulonephritis in patients with Staphylococcus aureus infection and (2) a membranoproliferative glomerulonephritis in patients with Staphylococcus epidermidis infection secondary to ventriculovascular shunts. In this study, we report a novel immunopathologic phenotype of immunoglobulin (Ig) A-dominant acute poststaphylococcal glomerulonephritis occurring in patients with underlying diabetic nephropathy. Five patients with type 2 diabetes presented with acute renal failure occurring after culture-positive staphylococcal infection. Renal biopsy disclosed an atypical pattern of acute endocapillary proliferative and exudative glomerulonephritis with intense deposits of IgA as the sole or dominant immunoglobulin, mimicking IgA nephropathy. The deposits were predominantly mesangial in distribution with few subepithelial humps. All five cases occurred superimposed on well-established diabetic nephropathy. Outcome was poor with irreversible renal failure in four of five (80%) cases. The possible pathophysiological basis of this atypical form of acute poststaphylococcal glomerulonephritis in diabetic patients is explored. Proper recognition of this entity is needed to avoid an erroneous diagnosis of IgA nephropathy, with corresponding therapeutic and prognostic implications.