Renal biopsy findings in patient #12 who had histological features on light microscopy and electron microscopy (EM) compatible with cryoglobulinemic glomerulonephritis. (a) A glomerulus on silver stain shows lobular accentuation due to mesangial hypercellularity and sclerosis. There is segmental duplication of the glomerular basement membrane (arrows) with associated cellular interposition (original magnification × 400). (b) A glomerulus on trichrome stain shows numerous intracapillary macrophages. A large subendothelial immune deposit is also seen (arrow) (original magnification × 600). (c) On EM, large subendothelial and mesangial electron dense deposits are seen. Glomerular peripheral capillaries are occluded by infiltrating monocytes/macrophages (original magnification × 3100). (d) A higher magnification image highlighting the large electron dense deposits in the subendothelial space that severely narrow the glomerular capillary lumen. A macrophage with intracellular phagocytized deposits and large phagolysosomes is seen (original magnification × 7830). Panels (e–g) show bright glomerular capillary wall and mesangial positivity for immunoglobulin G (IgG) (e) and kappa (f) with negative staining for lambda (g) by immunofluorescence on paraffin tissue after pronase digestion, corresponding to a monoclonal IgG kappa on serum immunofixation. The glomerular deposits were negative for IgG, IgA, C3, C1q, kappa, and lambda by routine immunofluorescence on frozen tissue (not shown) (original magnification × 400 for panels (e–g)).