amyloidosis

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A disorder characterized by the accumulation of an unusual extracellular fibrous protein (amyloid) in the connective tissue of the body. The deposition of amyloid may be widespread, involving major organs and leading to serious clinical consequences, or it may be very limited with little effect on health.

Amyloidosis has been classified clinically as: (1) primary amy-loidosis, with no evidence for preexisting or coexisting disease; (2) amyloidosis associated with multiple myeloma; (3) secondary amyloidosis, associated with chronic infections (such as osteomyelitis, tuberculosis, leprosy), chronic inflammatory disease (such as rheumatoid arthritis, ankylosing spondylitis, regional enteritis), or neoplasms (such as medullary carcinoma of the thyroid); (4) heredofamilial amyloidosis, associated with familial Mediterranean fever and a variety of heritable neuropathic, renal, cardiovascular, and other syndromes; (5) local amyloidosis, with local, often tumorlike, deposits in isolated organs without evidence of systemic involvement; (6) amyloidosis associated with aging. There is no specific treatment for amyloidosis, but supportive treatment is very useful.

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any of various pathological states in which the deposition of amyloid (def. 1) occurs in tissues. It is often associated with chronic infections and immunocyte dyscrasias. In the absence of medical intervention amyloid accumulates implacably, causing pressure atrophy of the affected tissue(s). Death subsequently results from interference with the normal physiological processes of affected vital organs. The descriptive term β-fibrillosis has been suggested for amyloidosis, after the beta-pleated sheet structure of the amyloid fibrils. Amyloidosis may be systemic, with major organ systems involved, or localized and restricted to a single organ. Many cases have a hereditary basis. It is now classified in terms of the protein that accumulates. See also amyloid A protein.

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The deposition in various tissues of amyloid. This protein is almost insoluble and once it infiltrates the tissues they become waxy and nonfunctioning. Systemic amyloidosis may be immunocytic or reactive (see below).

• cutaneous a. — multiple cutaneous, hard, painless, chronic plaques occur over the head, neck and shoulders of horses. There may be involvement of the nasal mucosa and resulting dyspnea.
• familial renal a. of Shar pei dogs — manifested by episodic fever and swelling of one or both hocks which may resolve spontaneously, but is recurring. The condition is resistant to treatment and eventually there is renal and/or hepatic failure.
• immunocytic a., immunogenic a., primary a. — amyloid produced from light chains of immunoglobulins as in plasma-cell dyscrasias. See also al protein.
• reactive a. — is derived from excess serum protein SAA produced as a result of chronic antigenic stimulation. The kidney is most often affected and the amyloid is most often deposited in glomeruli but medullary deposits are seen in cats and cattle. Idiopathic amyloidosis is common in the dog and less common in cats. It is associated with chronic suppurative disease processes in cattle, antiserum production in horses, and it occurs rarely in pigs. Called also secondary alopecia.
• renal a. — characterized by severe proteinuria and uremia. There is chronic diarrhea, polydipsia and anasarca. Seen particularly in dogs and cats.
• secondary a. — reactive amyloidosis (above).

(am′iloidō′sis)
n

A condition in which amyloid, a glyco-protein, is deposited intercellularly in tissues and organs. Four types of amyloidosis are recognized, two of which, primary amyloidosis and amyloid tumor, frequently produce nodules in the tongue and gingiva.

Amyloidosis. (Regezi/Sciubba/Jordan, 2003)