Membranoproliferative pattern in mixed cryoglobulinemia

Light micrograph in mixed cryoglobulinemia showing a membranoproliferative pattern with increased cellularity and thickening of the glomerular capillary walls. The pathognomonic finding is PAS-positive microthrombi composed of precipitated cryoglobulins that are occluding some of the capillary loops (arrows).

Light micrograph of a normal glomerulus. There are only one or two cells per capillary tuft, the capillary lumens are open, the thickness of the glomerular capillary wall (long arrow) is similar to that of the tubular basement membranes (short arrow), and the mesangial cells and mesangial matrix are located in the central or stalk regions of the tuft (arrows).