Franco Ferrario and Maria Pia Rastaldi
Dr Franco Ferrario
Renal Immunopathology Center
San Carlo Borromeo Hospital
DISTRIBUTION OF AMYLOID DEPOSITS
Amyloid deposition in the kidney can involve not only glomeruli and vessels, but also the interstitium and the tubular basement membranes, giving rise to several different morphological pictures.
There are cases of only minimal glomerular deposition, expressed by small mesangial nodules. Differential diagnosis has to be made from minimal change disease and some cases of IgA GN.
These very early cases need a careful demonstration of the few mesangial amyloid fibrils by electron microscopy.
A more intense mesangial amyloid deposition can be detected. Still to be differentiated from other mesangioproliferative nephritis.
In some cases, not only a more evident mesangial deposition, but also an initial involvement of the capillary walls can be detected.
When the deposits are massive, a “nodular form” is commonly found and has to be differentiated from other nodular glomerulonephritis, such as diabetic GS, light chain deposition disease and idiopathic MPGN. Amyloid specific stainings have to be performed in order to achieve a correct diagnosis (see part I ).
The deposition can be limited to the capillary walls. In these cases, a peculiar parallel orientation of amyloid fibrils forms argyrophilic subepithelial spikes. These spikes look like those found in MGN, although bigger and more irregularly distributed.
Subepithelial spikes due to amyloid deposition can be easily demonstrated by electron microscopy examination: fibrils are perpendicularly oriented and protrude towards the urinary space.
An almost exclusive arteriolar deposition can be rarely found.
Amyloid can deposit in the renal interstitium and in the tubular basement membranes. Congo Red staining, with its typical apple-green birefringence, confirms amyloid deposition in these kidney structures.
A massive deposition of amyloid can be detected in arteries and arterioles.
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