Amyloidosis (am-uh-loi-DO-sis) is a rare disease that occurs when a substance called amyloid builds up in your organs. Amyloid is an abnormal protein that is usually produced in your bone marrow and can be deposited in any tissue or organ. Amyloidosis can affect different organs in different people, and there are different types of amyloid. Amyloidosis frequently affects the heart, kidneys, liver, spleen, nervous system and digestive tract. Severe amyloidosis can lead to life-threatening organ failure.
Diagnosis of amyloidosis requires tissue biopsy. Biopsy is assessed for evidence of characteristic amyloid deposits. The tissue is treated with various stains. The most useful stain in the diagnosis of amyloid is Congo red, which, combined with polarized light, makes the amyloid proteins appear apple-green on microscopy. For example, in AL amyloidosis only 85% of people will have a positive fatpad biospy using Congo red stain. By comparison, rectal biopsy has sensitivity of 74-94%.
Amyloidosis is rare, the diagnosis is often delayed or the condition goes undiagnosed. Therefore, it is difficult to know exactly how many people are affected by this disease. However, researchers estimate that between 1,500 and 2,500 people develop AL amyloidosis each year in the United States. Hereditary and AA amyloidosis are much less common.