Medical Definition of Amyloid

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Amyloid: Any of a number of complex proteins that are deposited in tissues and that share selected laboratory features such as a change in the fluorescence intensity of certain aromatic dyes like Congo Red.

The deposition of amyloid occurs in a number of diseases. In many of these, there is disagreement as to whether amyloid causes the disease or is simply a sign of the disease downstream from the cause. (In Alzheimer's disease, those who believe that the deposition of beta-amyloid protein kills neurons are called baptists.)

Amyloid may be deposited widely in the body, as in systemic amyloidosis. Or the deposition of amyloid may be organ-specific and limited, for instance, to the pancreas, as in type 2 diabetes, or the central nervous system, as in Alzheimer's disease, Parkinson's disease, Huntington disease, Creutzfeldt-Jakob disease and bovine spongiform encephalopathy (mad cow disease).

The term amyloid comes from amylo- (starch) + -oid (like) = like starch. This reflects the mistaken identification of the substance as starch based on crude staining techniques.

Reviewed on 12/21/2018

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