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Pathologic Findings Light Microscopy

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Immunoglobulin A nephropathy and Henoch-Schönlein purpura nephritis can have any of the histologic phenotypes of immune complex-mediated glomerulonephritis other than pure membranous glomerulopathy, including no lesion by light microscopy with immune deposits by immunohis-tology, mesangioproliferative glomerulonephritis with mesangial but no endocapillary hypercellularity (Figs. 6.2 and 6.3), focal or diffuse proli-ferative glomerulonephritis with endocapillary hypercellularity (with or without crescents) (Fig. 6.4), overt crescentic glomerulonephritis with 50% or more crescents, type I membranoproliferative (mesangiocapillary) glo-merulonephritis (rare), and focal or diffuse sclerosing glomerulonephritis (7-10).

A variety of classification systems have been used to categorize the light microscopic phenotypes of IgA nephropathy, such as those proposed by

Figure 6.1. Immunofluorescence microscopy demonstrating glomerular mesan-gial staining for immunoglobulin A (IgA) in a patient with IgA nephropathy.

Kurt Lee et al (7) and by Mark Haas (8) (Table 6.1). Another approach is to use the same descriptive terminology that is in the World Health Organization (WHO) lupus classification system to categorize IgA nephropathy as well as other forms of immune complex glomerulonephritis. This system works as well for IgA nephropathy as it does for lupus, and also has the

Figure 6.2. Glomerulus from a patient with IgA nephropathy showing mild segmental mesangial hypercellularity in the upper left quadrant of the glomerulus [periodic acid-Schiff (PAS) stain].

Figure 6.3. Glomerulus from a patient with IgA nephropathy showing moderate segmental mesangial hypercellularity and increased mesangial matrix in the upper portion of the tuft (PAS stain).

advantage of not requiring knowledge of multiple different classification systems.

In patients whose renal biopsy specimens are referred to the University of North Carolina for evaluation, crescents are observed in about a third of patients with IgA nephropathy and two thirds of patients with Henoch-

Figure 6.4. Glomerulus from a patient with Henoch-Schönlein purpura showing a proliferative glomerulonephritis with endocapillary hypercellularity adjacent to a cellular crescent on the right of the tuft (Jones silver stain).

Note: The Lee and Haas systems were specifically designed for IgA nephropathy, whereas the terminology for the World Health Organization (WHO) system was designed for lupus glomerulonephritis but can be used to describe the pathology of IgA nephropathy.

Note: The Lee and Haas systems were specifically designed for IgA nephropathy, whereas the terminology for the World Health Organization (WHO) system was designed for lupus glomerulonephritis but can be used to describe the pathology of IgA nephropathy.

Schönlein purpura nephritis (11). However, overt crescentic glomerulonephritis with 50% of more of glomeruli with crescents is uncommon (< 5% in IgA nephropathy and <10% in Henoch-Schönlein purpura nephritis). When substantial crescent formation is present, especially with conspicuous fibrinoid necrosis, the possibility of concurrent antineutrophil cytoplasmic antibody (ANCA) disease should be considered (12).

Between 5% and 10% of specimens with IgA nephropathy identified by immunohistology have focal segmental glomerular sclerosis as seen on light microscopy that is indistinguishable from idiopathic focal segmental glomerulosclerosis (8).

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