Amyloidosis

Amyloidosis

Amyloids are extracellular abnormally folded glycoproteins that are resistant to proteolysis.

The deposition of amyloids within extracellular spaces of tissues and organs results in a diverse group of conditions known as amyloidosis.

Gross appearance

q  Small amount of amyloids are not visible.

q  Large amount of amyloids appears as firm, white, opaque deposits. Mainly deposits in spleen, liver, kidney.

q  In spleen- Sago spleen: When amyloids deposit as discrete nodules of firm, white mass over the surface resembling Tapioca grains (sago).

q  Liver appears larger, paler and firmer than normal.

Microscopic appearance

q In H & E stain, amyloids appear as irregular globular or linear masses of eosinophilic hyaline materials.

q Special stain is Congo red. Orange red color in ordinary microscope.

Classification of amyloidosis

Four main categories of amyloidosis are-

1.      Immunocyte associated amyloidosis (primary)

This form can be localized or systemic and affects more than one tissue. Here, amyloid is the immunoglobulin light chain (AL amyloidosis) produced in excess by plasma cells (hence the name immunocyte associated).

The systemic form can be associated with a form of bone cancer known as multiple myeloma (plasma cell tumor).

Myeloma cells produce only abnormal light chain IgG. These light chains come together to form amyloid deposits in different organs which can cause serious damage to these organs. Abnormal light chains in blood and urine are sometimes referred to as "Bence Jones protein".

2. Reactive systemic amyloidosis (Secondary)

This form is associated with chronic inflammatory diseases like tuberculosis.

In chronic inflammatory diseases, macrophages secret cytokines (IL1, IL2, TNF) which stimulate hepatocytes to produce Serum amyloid A (SAA) protein. SAA deposits extracellularly.

3. Senile amyloidosis

Amyloidosis in old age in man and animals.

4. Familial amyloidosis

It is determined by genetic factor and is found in human beings, mice, dogs and cats.