MORPHOLOGY
Main Organs Involved
• Secondary amyloidosis: Kidneys, liver, spleen, lymph nodes, adrenals and thyroid.
• Primary amyloidosis: Heart, GI tract, respiratory tract, peripheral nerves, skin and
tongue.
Gross
• May or may not be apparent grossly.
• If large amount accumulates → affected organs are enlarged, firm and have a waxy
appearance (Fig. 6.24A).• Cut surface: If the amyloid deposits are large, painting the cut surface with iodine gives
a yellow color, which is transformed to blue violet after application of sulfuric acid
(which acidifies iodine). This method was used for demonstrating cellulose or starch.
This staining property was responsible for the coining of the term amyloid (starch-like).
But it is neither starch nor cellulose.
Microscopy
Q. Write short note on special stains for amyloid.
Hematoxylin and Eosin Stain
• Amyloid deposits are always extracellular (Fig. 6.25A) and begin between the cells. In
AL form, perivascular and vascular deposits are common.
• Progressive accumulation of amyloid produces pressure atrophy of adjacent cells.
• Appears as an amorphous, eosinophilic, hyaline, glassy, extracellular substance.
• Many other substances (e.g., collagen, fibrin) also stain eosinophilic with hematoxylin
and eosin. Hence, it is necessary to differentiate amyloid from these other hyaline
deposits by using special stains.
Staining (Tinctorial) Properties of Amyloid
1. Congo-red stain: It is the special stain used for the diagnosis of amyloidosis. Amyloid
stains pink or red with the Congo-red dye under ordinary light (Fig. 6.25B). But more
specific when viewed under polarizing microscope; amyloid gives apple-green
birefringence (Fig. 6.25C). This reaction is due to the cross-β-pleated configuration of
amyloid fibrils. Can be confirmed by electron microscopy.
2. Van Gieson stains: It takes up khaki color.
3. Alcian blue: It imparts blue color to glycosaminoglycans in amyloid.
4. Periodic acid-Schiff (PAS) reaction: It stains pink.
5. Methyl violet and cresyl violet: These metachromatic stains (belong to rosanilin group
of basic dyes) give rose pink color to the amyloid deposits whereas surrounding tissue is
colored blue.
6. Iodine solution produces a dark, mahogany brown color when poured over the cut
surface of the organ involved by amyloidosis. It is transformed to blue violet after
application of sulfuric acid.
7. Thioflavin T: It is not specific for amyloid, but amyloid fluoresce when viewed in
ultraviolet light.
8. Immunohistochemical staining: It can distinguish AA, AL and ATTR types.
MORPHOLOGY OF MAJOR ORGANS INVOLVED
Q. Describe the gross and microscopic features
of organs involved in primary/secondaryamyloidosis.
Morphology of major organs involved in primary and/or secondary amyloiodosis is discussed
below:
Kidney
Kidney involvement is the most common and the most serious form of organ involvement.
• Gross (Fig. 6.24A): It may be of normal size and color during early stages. In advanced
stages, it may be shrunken due to ischemia, which is caused by vascular narrowing
induced by
• Microscopy: Most commonly renal amyloid is of light-chain (AL in primary
amyloidosis) or AA (in secondary amyloidosis type).
– Glomeruli: It is the main site of amyloid deposition(Fig. 6.24B).
◆ First, focal deposits within mesangial matrix, accompanied by diffuse or
nodular thickening of the glomerular basement membranes.
◆ Later, both the mesangial and basement membranes deposits cause capillary
narrowing. Progressive accumulation of amyloid results in obliteration of the
capillary lumen and glomerulus shows broad ribbons of amyloid.
• Amyloid may also be deposited in the peritubular interstitial tissue, arteries and
arterioles. the amyloid deposit within arterial and arteriolar walls.
Spleen
Q. Describe the gross and microscopic
appearance of spleen in amyloid (Sago and
Lardaceous spleen).
• Gross: It may be normal in size or may cause moderate to marked splenomegaly (200–
800 g). It may show one of two patterns of deposition.
– Sago spleen: Amyloid deposits are limited to the splenic follicles, which grossly
appear like tapioca/sago granule; hence known as sago spleen. Microscopically,
the amyloid is deposited in the wall of arterioles in the white pulp.
– Lardaceous spleen: Amyloid is deposited in the walls of the splenic sinuses and
connective tissue framework in the red pulp. This may result in moderate to marked
enlargement of spleen. Fusion of the early deposits give rise to large, map-like areas
of reddish color on cut surface. This resembles pig fat (lardaceous) and hence called
as lardaceous spleen. Microscopically, it shows amyloid deposits in the wall of the
sinuses.
• Light microscopy: These deposits appear homogenous pink, which when stained with
Congo-red and viewed under polarizing microscope, give rise to characteristic green
birefringence.
Liver• Gross: It may cause moderate to marked enlargement. In advance stages, it appears pale,
gray and waxy.
• Microscopy
– Amyloid first deposits in the space of Disse and then progressively encroaches on
adjacent hepatic parenchymal cells and sinusoids.
– Progressive accumulation leads to deformity, pressure atrophy and disappearance of
liver cells.
Heart
• It may be involved in systemic amyloidosis (AL type) or may be the major organ
involved in senile systemic amyloidosis.
• Gross: Heart may be enlarged and firm. Subendocardial deposits may appear as gray-
pink like dew-drop.
• Microscopy
– Myocardium: Amyloid is deposited between the muscle fibers and their progressive
accumulation causes pressure atrophy of myocardial fibers.
Other Organs
They may be involved in systemic disease and include adrenals, thyroid and pituitary.
Nodular deposits in the tongue may cause macroglossia. In concise points for exam