Page 105 - Textbook of Pathology, 6th Edition

89 CHAPTER 4

Figure 4.12 Amyloidosis of kidney. The amyloid deposits are seen mainly in the glomerular capillary tuft. The deposits are also present in
peritubular connective tissue producing atrophic tubules and amyloid casts in the tubular lumina, and in the arterial wall producing luminal narrowing. Immunopathology Including Amyloidosis

extracellular matrix and within the basement membranes of In the glomeruli, the deposits initially appear on the
blood vessels. basement membrane of the glomerular capillaries, but
later extend to produce luminal narrowing and distortion
Grossly, the affected organ is usually enlarged, pale and of the glomerular capillary tuft. This results in abnormal
rubbery. Cut surface shows firm, waxy and translucent increase in permeability of the glomerular capillaries to
parenchyma which takes positive staining with the iodine macromolecules with consequent proteinuria and
test.
nephrotic syndrome.
Microscopically, the deposits of amyloid are found in the In the tubules, the amyloid deposits likewise begin close
extracellular locations, initially in the walls of small blood to the tubular epithelial basement membrane. Subse-
vessels producing microscopic changes and effects, while quently, the deposits may extend further outwards into
later the deposits are in large amounts causing the intertubular connective tissue, and inwards to produce
macroscopic changes and effects of pressure atrophy. degenerative changes in the tubular epithelial cells and
amyloid casts in the tubular lumina.
Based on these general features of amyloidosis, the salient
pathologic findings of major organ involvements are Vascular involvement affects chiefly the walls of small
described below. arterioles and venules, producing narrowing of their
lumina and consequent ischaemic effects.
Amyloidosis of Kidneys
Amyloidosis of the kidneys is most common and most
serious because of ill-effects on renal function. The deposits
in the kidneys are found in most cases of secondary
amyloidosis and in about one-third cases of primary
amyloidosis. Amyloidosis of the kidney accounts for about
20% of deaths from amyloidosis. Even small quantities of
amyloid deposits in the glomeruli can cause proteinuria and
nephrotic syndrome.

Grossly, the kidneys may be normal-sized, enlarged or
terminally contracted due to ischaemic effect of narrowing
of vascular lumina. Cut surface is pale, waxy and
translucent (Fig. 4.11).
Microscopically, amyloid deposition occurs primarily in
the glomeruli, though it may involve peritubular Figure 4.13 Amyloidosis kidney, Congo red stain. A, The amyloid
interstitial tissue and the walls of arterioles as well deposits are seen mainly in the glomerular capillary tuft stained red-pink
(Fig. 4.12): (Congophilia). B, Viewing the same under polarising microscopy, the
congophilic areas show apple-green birefringence.