Histology of Renal Lesions in Dysproteinemias

FIGURE 11-35 (s

Light chain amyloidosis. Amyloid deposits associated with dysproteinemias are predominantly composed of fragments of the light chain variable region (AL amyloidosis) and very rarely of fragments of heavy chain variable regions (AH amyloidosis) [74]. On light microscopy, this type of amyloid is indistinguishable from amyloid of other origin. The homogeneous and amorphous material, faintly pink-stained with eosin or sometimes brownish-stained with methenamine silver, is deposited in the mesangium and along the capillary loops of the glomeruli, in the vessels, and occasionally in the interstitium. Amyloid frequently is localized in the glomerular basement membrane (GBM) as sheaths of fibrils or spicules that are larger and more irregularly arranged than are the spikes in membranous glomerulopathy. Congo red-stained sections viewed under polarized light reveal the specific apple-green birefringence, the gold standard for the diagnosis. Amyloid deposits are sometimes stained with commercially available antisera against light chains. In addition, these deposits also are positive for amyloid P, heparan sulfate proteoglycan, and apolipoprotein E. On electron microscopy, amyloid is composed of long, randomly distributed, nonbranching fibrils with diameters of 8 to 12 nm.

A, Amyloid deposits in mesangium and the capillary wall (arrows: spicules).

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FIGURE 11-37 (see Color Plate)

Light chain deposition disease. In about 60% of patients with this renal lesion, nodular expansion of the mesangium is seen that resembles nodular diabetic nephropathy [75,76]. The nodules stained purple with periodic acid-Schiff (PAS) stain have a homogeneous appearance, and those stained with methenamine silver are pink-brownish in color. In a few cases, a more mesangiocapillary pattern of injury is present. The tubular basement membranes (TBMs) are

FIGURE 11-35 (Continued)

B, Amyloid deposits in the renal arteries in a congo red-stained slide and viewed under polarized light. Amyloid has an apple-green color. C, Immunofluorescence. Amyloid deposits in the mesangium stained with anti-X antibodies. (Panel A, methena-mine silver. Original magnification X550, X350, X400, respectively.)

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