Light, immunofluorescence, and electron microscopy in immuno-globulin A (IgA) nephropathy. IgA nephropathy is a chronic glomerular disease in which IgA is the dominant or sole component of deposits that localize in the mesangial regions of all glomeruli. In severe or acute cases, these deposits also are observed in the capillary walls. This disorder may have a variety of clinical presentations. Typically, the presenting features are recurrent macroscopic hematuria, often coincident with or immediately after an upper respiratory infection, along with persistent microscopic hematuria and low-grade proteinuria between episodes of gross hematuria. Approximately 20% to 25% of patients develop end-stage renal disease over the 20 years after onset. A, On light microscopy, widening and often an increase in cellularity in the mesangial regions are observed, a process that affects the lobules of some glomeruli to a greater degree than others. This feature gives rise

to the term focal proliferative glomerulonephritis. In advanced cases, segmental sclerosis often is present and associated with massive proteinuria. During acute episodes, crescents may be present.

B, Large round paramesangial fuchsinophilic deposits often are identified with Masson's trichrome or other similar stains (arrows).

C, Immunofluorescence defines the disease; granular mesangial deposits of IgA are seen with associated complement C3, and IgG or IgM, or both. IgG and IgM often are seen in lesser degrees of intensity than is IgA. D, On electron microscopy the abnormalities typically are those of large rounded electron-dense deposits (arrows) in paramesangial zones of most if not all lobules. Capillary wall deposits (subepithelial, subendothelial, or both) may be present, especially in association with acute episodes. In addition, capillary basement membranes may show segmental thinning and rarefaction.

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