Incidental healed postinfectious glomerulonephritis: a study of 1012 renal biopsy specimens examined by electron microscopy.

Glomerulonephritis (GN) characterized by immune complex deposits typical of postinfectious GN but with a paucity or absence of overt clinical symptoms and/or urinary abnormalities may occur after a group A streptococcus infection. The overall incidence of this type of subclinical GN is not known. To address this question, electron microscopy findings in 1012 consecutive renal biopsy specimens (952 native kidney, 60 transplant) examined by a single renal pathologist from August 1999 to April 2002 were retrospectively reviewed for the presence of distinct subepithelial and intramembranous deposits indicative of postinfectious GN. Such deposits were noted in 83 biopsy specimens, including 26 with a primary diagnosis of postinfectious GN (acute, persistent, or latent) and 57 in which these deposits were an incidental finding. In each of the latter 57 cases, some or all of the deposits showed partial or extensive loss of electron density typical of partially or largely resorbed deposits. A diagnosis of incidental postinfectious GN was not made in any biopsy specimen exhibiting another immune complex-related glomerular disease that could possibly account for the deposits, composing 443 of the 1012 biopsy specimens examined. Thirty of the 57 biopsy specimens with incidental postinfectious GN showed mesangial hypercellularity, although this was focal and segmental in all but 3 cases and was not accompanied by the endocapillary hypercellularity typical of acute postinfectious lesions. Immunofluorescence microscopy revealed glomerular deposits of C3 in >90% of these biopsy specimens and IgM deposits in 66%, but only rare IgG, IgA, and Cq deposits. Twenty-three (40%) of these 57 biopsy specimens exhibited diabetic nephropathy, either alone or in combination with another lesion; for perspective, only 128 (13%) of the 1012 biopsy specimens examined showed evidence of diabetic nephropathy. In summary, incidental evidence of resolving or largely healed postinfectious GN was noted in up to 10.5% of renal biopsy specimens (57 of 543, not including specimens with a primary diagnosis of an immune complex-related glomerular disease). The recognition of such lesions is potentially important in the interpretation of certain renal biopsy specimens.
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