Thickening of glomerular capillary walls: a guide to differential diagnosis by electron microscopy

Thickening of capillary walls is a feature of many glomerular diseases. Widening of the wall may be produced by deposits and other changes affecting either subepithelial and subendothelial regions or the glomerular basement membrane itself. Careful light microscopic examination using special stains can distinguish some patterns of capillary wall thickening, but electron microscopy is needed to demonstrate most lesions clearly. In this brief review, a guide to the major causes for capillary wall thickening is discussed, using a simple classification, and some of the patterns are illustrated. Precise delineation of the capillary wall changes in glomerular diseases is important to insure accurate classification and a clear understanding of pathogenetic mechanisms.