Amyloidosis

Introdcution

Amyloid infiltration occurs in all species - amaloid is an inert substance that becomes deposited under the endothelium and basement membranes of a variety of tissues, notably the renal glomeruli, Islets of Langerhans in the pancreas and the liver (between the sinusoidal reticulum and the hepatic cords).

Causes

May be a primary condition or appear secondary to some chronic tissue destructive process such as:

• an infectious process elsewhere in the body
• sustained antigenic stimulation, eg repeated injections with an antigenic substance or production of excessive antibody by leukocytes

Gross Pathology

Affected organs will apear:

• pale (greyish waxy appearance)
• enlarged with rounded edges
• firm
• very prone to rupture

Microscopically

• deposition of amyloid in the space of Disse (or perisinusoidal space) which is in the liver between the hepatocytes and a sinusoid.
• shows 'apple-green' fluorescence under polarised light after staining with Congo Red

Arterial

Amyloid is an eosinophilic, homogenous, hyaline material. Due to its beta-pleated-sheet structure it is almost insoluble. Amyloid may be:

• AA: Serum amyloid A, alpha-2 globulin.
• AL: Derived from immunoglobulin light chains.

Disease may be truly idiopathic (dogs and cats) or may be secondary to another disease process, often chronic inflammation or neoplasia. Chronic antigenic stimulation induces the overproduction of AA protein which may become deposited throughout the body.

Deposits are found in:

• Renal vessels and glomeruli.
• Splenic white pulp.
• Space of Disse.
• Coronary arteries.
• Meningeal arteries.

Affected organs are non-functional and appear waxy and pale.

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