Lichen Amyloidosis

Updated: Dec 11, 2015
  • Author: Sultan Al-Khenaizan, MBBS, FRCPC; Chief Editor: William D James, MD  more...
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Overview

Background

Amyloidosis is a generic term that signifies the abnormal extracellular tissue deposition of one of a family of biochemically unrelated proteins that share certain characteristic staining properties, including apple-green birefringence of Congo red–stained preparations viewed under polarizing light. Under electron microscopy (EM), amyloid deposits are composed of linear, nonbranching, aggregated fibrils, 7.5-10 nm thick of indefinite length arranged in a loose meshwork.

X-ray diffraction crystallography and infrared spectroscopy revealed that these fibrils have a meridional, antiparallel, beta-pleated sheet configuration with polypeptide chains arranged perpendicular to the long axis of the fibrils. [1]

Amyloid deposits contain (in addition to the fibrillar component) a nonfibrillar protein referred to as amyloid-P (Am-P). This protein is identical to normal plasma globulin, known as serum amyloid-P (SAP). Am-P constitutes 14% of the dry weight of amyloid. This protein is also found in the microfibrillar sheath of elastic fibers. SAP is closely related to the acute phase reactant C-reactive protein (CRP) and has been shown to be an elastase inhibitor.

SAP and the beta-pleated sheet configurations are thought to protect amyloid deposits from degradation and phagocytosis, leading to persistence of the deposits.

Lichen amyloidosis has been reported in association with few syndromes. The most intriguing is the association with multiple endocrine neoplasia type 2A (MEN 2A), also known as Sipple syndrome. [2, 3, 4, 5, 6, 7, 8, 9, 10] The cardinal triad of this autosomal dominant syndrome is medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism. Many cases of familial lichen amyloidosis were reported in families with MEN 2A. The lichen amyloidosis in this syndrome is usually localized to the interscapular region consisting of lichenoid papules, with hyperpigmentation and fine scaling. The histopathologic and immunohistochemistry findings are similar to those in isolated lichen amyloidosis, pointing to keratin-derived amyloidosis.

A single case of lichen amyloidosis in Alagille syndrome has been reported. [11] This consists of interlobular biliary duct deficiency and cardiovascular, vertebral, and ocular anomalies.

The disease is associated with marked pruritus secondary to cholestasis. This is believed to be the cause of the amyloid deposition.

Maddison et al suggest a possible cause of the severe pruritus associated with lichen amyloidosis in relation to nerve fiber density. They suggest the hypersensitivity of the remaining nerve fibers is a response to an unexplained neurodegeneration of the absent nerve fibers. [12]

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Pathophysiology

Amyloid deposits in macular amyloidosis and lichen amyloidosis bind to antikeratin antibodies. These deposits contain sulfhydryl groups, pointing to altered keratin as a source for these deposits. Apaydin et al found no differences in staining characteristics of cytokeratins between macular amyloidosis and lichen amyloidosis. [13] Interestingly, in their study, all the cytokeratins detected in amyloid deposits were of basic type (type II). This may be because, in amyloidogenesis, acidic cytokeratins such as cytokeratin 14 are degraded faster than basic types.

Weyers et al presented a convincing argument that the deposition of amyloid in lichen amyloidosis is not the cause but the result of itching and scratching. This argument was based on several lines of evidence. [14]

Amyloid deposition per se does not cause itching. Systemic amyloidosis is not associated with pruritus. Nonpruritic lichen amyloidosis has also been described. Pruritus usually precedes the development of lichen amyloidosis by years. Amyloid cannot be detected in clinically healthy skin of patients with lichen amyloidosis.

Striking similarities, both clinically and histopathologically, exist between lichen amyloidosis and lichen simplex chronicus.

A pathogenic missense mutation was identified in the OSMR gene that encodes the oncostatin M (OSM) receptor β (OSMR-β) in a Brazilian pedigree. [15]

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Epidemiology

Race

Lichen amyloidosis is believed to be more common in persons of Chinese ancestry than in other people.

Sex

Lichen amyloidosis is more common in males than in females.

Age

Lichen amyloidosis occurs most frequently in persons aged 50-60 years.

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