In diabetes, basement membranes of majority of capillaries in the body are thickened by deposits of nonenzymatic glycosilated proteins (diabetic microangiopathy): retinopathy, coronary arteries, and peripheral vessels.
In kidney, diabetic nephropathy includes : diabetic glomerulosclerosis, arteriolosclerosis and papillary necrosis, with an increased risk for pyelonephritis.
Diabetic glomerulosclerosis is characterized by thickening of glomerular basement membrane with increased permeability. With time, the mesangial space becomes larger by deposits of proteins (collagen IV), initially diffuse, then nodular.
Diffuse diabetic glomerulosclerosis. The deposits appear diffusely on the basement membranes of capillary loops of the glomeruli, as well as on basement membranes of tubules and arterioles. (PAS, ob. x40)
In nodular diabetic glomerulosclerosis, PAS-positive nodular deposits (containing mucopolysaccharides, fibrils and collagen) may appear in the mesangial space, at the periphery of the glomerulus, pushing the capillaries. The lesion is focal (glomeruli are not entirely affected), and some of them are spared. This pattern is also called Kimmelstiel-Wilson lesion. (PAS, ob. x20)