Lichen Amyloidosis

Updated: Oct 24, 2017
  • Author: Sultan Al-Khenaizan, MBBS, FRCPC; Chief Editor: William D James, MD  more...
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Overview

Practice Essentials

Primary localized cutaneous amyloidosis (PLCA) is characterized by extracellular deposition of heterogenic amyloid proteins in the skin without systemic involvement. Types of PLCA include the following:

  • Lichen amyloidosis
  • Macular amyloidosis
  • Nodular amyloidosis

Lichen amyloidosis is believed to be more prevalent among Southern Chinese and South American populations. [7]  It is more common in males than in females and occurs most frequently in persons aged 50-60 years.

Lichen amyloidosis accounts for approximately 10% of cases of PLCA. The pathogenesis remains undetermined, but it is considered a secondary process following chronic scratching associated with primary disease. [1]

A rare variant of multiple endocrine neoplasia type 2A (MEN 2A) is associated with lichen amylosidosis. The cardinal triad of this autosomal dominant syndrome is medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism. 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. [2]

Maddison et al suggest a possible cause of the severe pruritus associated with lichen amyloidosis in relation to nerve fiber density. They suggest that the hypersensitivity of the remaining nerve fibers is a response to an unexplained neurodegeneration of the absent nerve fibers. [3]

The diagnosis can usually be made clinically, particularly in patients with the classic presentation. A skin biopsy should be reserved for evolving lesions. Lichen amyloidosis is a chronic condition without potential for malignant transformation or increase in mortality. Treatment is not required but can be employed for symptomatic or cosmetic complaints. Many therapeutic modalities have been suggested, including topical and systemic medications, phototherapy, electrodessication, dermabrasion, cryosurgery, and lasers, but no standardized treatment has been established. [4]

Lichen amyloidosis is a chronic condition without potential for malignant transformation or increase in mortality. Treatment is not required but can be employed for symptomatic or cosmetic complaints. Complications are usually related to pruritus with bleeding from excessive scratching. 

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Pathophysiology

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 that are 7.5-10 nm thick and of indefinite length and 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. [5]

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.

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. [6] 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. [1]

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.

Small-fiber neuropathy (SFN) has been found in patients with lichen amyloidosis and pruritus. An increase in epidermal expression of IL-31 receptors in the skin was also found. SFN results in a reduction of intraepidermal nerve fibers (IENF), and pruritus may be associated with hypersensitivity of cutaneous nerve fibres related to the increased expression of epidermal IL-31 receptors. [7]

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. [8]

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