Anatomic Pathology: Renal Pathology

389) A 17-year-old Asian girl has microscopic hematuria, transient gross hematuria at the time of an upper respiratory infection, 1 g/day proteinuria, normal serum albumin, and normal renal function. Serologic evaluation reveals normal serum complement levels, negative antinuclear antibody (ANA), and negative antistreptolysin O. Light microscopy demonstrates a pattern of diffuse mesangial proliferation, and electron microscopy demonstrates mesangial electron-dense deposits. The diagnostic immunofluorescence image is shown. Which immunofluorescence stain does the image represent?

• IgA nephropathy is the most common glomerular disease worldwide and is particularly common in Asian patients.

• IgA nephropathy typically manifests with microscopic hematuria, low-grade proteinuria, and normal renal function. Transient gross hematuria may occur simultaneously with an upper respiratory tract infection (“synpharyngitic gross hematuria”). Serum antinuclear antibody (ANA) and complement levels are normal.

• End-stage renal disease occurs in approximately 30% of patients with IgA nephropathy.

• Most cases of IgA nephropathy are idiopathic in origin (i.e., primary). The pathogenesis is thought to involve defective galactosylation of IgA molecules, making the IgA molecules prone to deposition in the mesangium where they trigger inflammatory and fibrogenic pathways.

• Secondary causes of IgA nephropathy include chronic liver disease (in which there is decreased hepatic clearance of IgA), chronic inflammatory gastrointestinal and skin diseases (which are associated with increased mucosal IgA secretion), and HIV infection.

Tumlin JA, Madaio MP, Hennigar R: Idiopathic IgA nephropathy: pathogenesis, histopathology, and therapeutic options. Clin J Am Soc Nephrol 2007;2(5):1054-1061.

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