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. 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. Also, thioflavin T stain may be used.An abdominal fat biopsy is not completely sensitive and so, sometimes, biopsy of an involved organ (such as the kidney) is required to achieve a diagnosis. 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%.
A detailed elaboration of the pathogenesis of AL amyloidosis is beyond the scope of this article, but a few points warrant discussion. A key feature of all types of amyloidosis is abnormal folding of a protein that is normally soluble. Organ dysfunction results from disruption of tissue architecture by amyloid deposits. However, increasing evidence indicating that amyloidogenic precursor proteins or precursor aggregates have direct cytotoxic effects that also contribute to disease manifestations is emerging.