Chapter 48. The Kidney: II. Glomerular Diseases

This group of renal diseases is characterized by primary abnormalities of the glomerulus, both structural (inflammation, cellular proliferation, basement membrane thickening, fibrosis, epithelial cell changes) and functional (increased permeability causing pro-teinuria or hemorrhage of glomerular origin). Glomerular diseases may be congenital or acquired. Congenital glomerular diseases (the most common being Alport's syndrome, in which nephritis is associated with nerve deafness and cataract) are very rare. This chapter deals with acquired glomerular diseases.

The classification of glomerulonephritis uses a combination of clinical (congenital or acquired; acute or chronic), morphologic (proliferative, membranous, minimal change), and immunologic criteria (Table 48-1).

Pathologic Changes

Glomerular diseases may be focal, showing abnormality in some but not all the glomeruli; or diffuse, where all glomeruli are affected. In segmental glomerular involvement, only a portion of each individual glomerulus is affected, in contrast to a global change, which involves entire glomeruli. Combinations of these terms are commonly used; eg, in focal segmental involvement the abnormality is present in some but not all glomeruli and the affected glomeruli are only partially involved.

Identification of exact morphologic changes in the glomerulus in renal biopsy specimens is important in the differential diagnosis of glomerular diseases (Figure 48-1). Some knowledge of these changes is necessary because different glomerular diseases show varying combinations of these same basic features.

Proliferation of Cells in the Glomerulus

Any of the different cell types in the glomerulus may undergo proliferation in different diseases.

1. Mesangial cell proliferation is recognized by the presence of increased numbers of nuclei (in excess of three) in the central part of a glomerular lobule. Mesangial cells are part of the phagocytic mechanism of the glomerulus.

2. Endothelial cell proliferation causes obliteration of the capillary lumen.

3. Epithelial cell proliferation, when extensive, leads to formation of a crescent-shaped mass of cellular or collagenized tissue that obliterates Bowman's space. Epithelial cell proliferation is believed to be stimulated by fibrin deposition in Bowman's space.

Infiltration of the Glomerulus by Inflammatory Cells

Infiltration with neutrophils, ...