Page 104 - Textbook of Pathology, 6th Edition

88 Metachromatic stains employed are rosaniline dyes such as produce symptoms and may even cause death. The diagnosis
methyl violet and crystal violet which impart rose-pink of amyloid disease can be made from the following
colouration to amyloid deposits. However, small amounts investigations:
of amyloid are missed, mucins also have metachromasia and 1. BIOPSY EXAMINATION. Histologic examination of
that aqueous mountants are required for seeing the biopsy material is the commonest and confirmatory method
preparation. Therefore, this method has low sensitivity and for diagnosis in a suspected case of amyloidosis. Biopsy of
lacks specificity. an obviously affected organ is likely to offer the best results
4. CONGO RED AND POLARISED LIGHT. All types of e.g. kidney biopsy in a case of dialysis, sural nerve biopsy in
amyloid have affinity for Congo red stain; therefore this familial polyneuropathy. In systemic amyloidosis, renal
SECTION I
method is used for confirmation of amyloid of all types. The biopsy provides the best detection rate, but rectal biopsy also
stain may be used on both gross specimens and microscopic has a good pick up rate. However, gingiva and skin biopsy
sections; amyloid of all types stains pink red colour. If the have poor result. Currently, fine needle aspiration of
stained section is viewed in polarised light, the amyloid abdominal subcutaneous fat followed by Congo red staining
characteristically shows apple-green birefringence due to cross- and polarising microscopic examination for confirmation has
β-pleated sheet configuration of amyloid fibrils. The stain become an acceptable simple and useful technique with
can also be used to distinguish between AL and AA amyloid excellent result.
(primary and secondary amyloid respectively). After prior 2. IN VIVO CONGO RED TEST. A known quantity of
treatment with permanganate or trypsin on the section, Congo red dye may be injected intravenously in living
Congo red stain is repeated—in the case of primary amyloid patient. If amyloidosis is present, the dye gets bound to
(AL amyloid), the Congo red positivity (congophilia) amyloid deposits and its levels in blood rapidly decline. The
persists,* while it turns negative for Congo red in secondary test is, however, not popular due to the risk of anaphylaxis
amyloid (AA amyloid). Congo red dye can also be used as to the injected dye.
an in vivo test (described below).
3. OTHER TESTS. A few other tests which are not
5. FLUORESCENT STAINS. Fluorescent stain thioflavin- diagnostic but are supportive of amyloid disease are protein
T binds to amyloid and fluoresce yellow under ultraviolet electrophoresis, immunoelectrophoresis of urine and serum,
light i.e. amyloid emits secondary fluorescence. Thioflavin- and bone marrow aspiration.
S is less specific.
6. IMMUNOHISTOCHEMISTRY. More recently, type of MORPHOLOGIC FEATURES OF
amyloid can be classified by immunohistochemical stains. AMYLOIDOSIS OF ORGANS
General Pathology and Basic Techniques
Various antibody stains against the specific antigenic Although amyloidosis of different organs shows variation
protein types of amyloid are commercially available. in morphologic pattern, some features are applicable in
However, most useful in confirmation for presence of general to most of the involved organs.
amyloid of any type is anti-AP stain; others for determining
the biochemical type of amyloid include anti-AA, anti-lambda Sites of Amyloid Deposits. In general, amyloid proteins get
(λ), anti- kappa (κ) antibody stains etc. filtered from blood across the basement membrane of
vascular capillaries into extravascular spaces. Thus, most
7. NON-SPECIFIC STAINS. A few other stains have been commonly amyloid deposits appear at the contacts between
described for amyloid at different times but they lack the vascular spaces and parenchymal cells, in the
specificity. These are as under:
i) Standard toluidine blue: This method gives orthochromatic
blue colour to amyloid which under polarising microscopy
produces dark red birefringence. However, there are false
positive as well as false negative results; hence not
recommended.
ii) Alcian blue: It imparts blue-green colour to amyloid
positive areas and is used for mucopolysaccharide content
in amyloid but uptake of dye is poor and variable.
iii) Periodic acid Schiff (PAS): It is used for demonstration
of carbohydrate content of amyloid but shows variable
positivity and is not specific.

DIAGNOSIS OF AMYLOIDOSIS
Amyloidosis may be detected as an unsuspected morpho-
logic finding in a case, or the changes may be severe so as to

Figure 4.11 Amyloidosis of kidney. The kidney is small and pale in
*Easy way to remember: Three ps i.e. there is persistence of colour. Sectioned surface shows loss of cortico-medullary distinction
congophilia after permanganate treatment in primary amyloid. (arrow) and pale, waxy translucency.