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INTRODUCTION

KEY POINTS

  • Amyloidosis is the deposition of amyloid, a group of unrelated proteins, in the extracellular space of various organs and tissues of the body.

  • Amyloidosis is divided into primary systemic and localized cutaneous types.

  • Primary cutaneous amyloidosis is subdivided into nodular, macular, and lichen types.

  • Individuals with skin of color, particularly Asians, Arabs, and South Americans, appear to be predisposed to developing lichen amyloidosis.

  • A review of common dermatologic diagnoses lists lichen amyloidosis as one of the 12 most common skin disorders affecting those of Asian ethnicity.

  • The treatment options for amyloidosis are palliative, not curative, and alleviate the symptoms of pruritus.

The term amyloid was coined in 1838 by Schleiden, a German botanist, to describe cellulose-like substances in plants.1 Amyloidosis refers to the deposition of amyloid, a group of unrelated proteins in the extracellular space of various organs and tissues of the body, which leads to a pathologic change. Eosinophilic amorphous substances are seen through the use of a light microscope, and amyloid subtypes are composed of 7.5- to 10-nm-wide linear, nonbranching tubular fibrils. These are arranged in a meshwork pattern,2 and each fibril has a β-pleated sheet configuration. However, the quaternary structure of these amyloids is not yet understood.3

Several classifications of amyloidosis exist. The original classification system divides the condition into primary or secondary types of either systemic or localized amyloidosis. Another more recent classification scheme designates amyloidosis as either acquired or hereditary. The clinical subtype will depend on the type of amyloid fibril protein that is deposited.

Systemic amyloidosis can be primary (AL) or secondary (AA). It can also be associated with other processes such as hemodialysis.4 In primary systemic amyloidosis, the type of amyloid deposited is the immunoglobulin variable fragment designated as AL amyloid.4,5 Serum amyloid A deposition is the cause of systemic AA amyloidosis. This form is typically associated with chronic inflammatory conditions such as Crohn disease, rheumatoid arthritis, dermatomyositis, cystic fibrosis, and lupus.4 The skin can be variably affected in systemic amyloidosis. The cutaneous signs, which are more indicative of systemic involvement, include hemorrhages, waxy papules that are pruritic and/or hemorrhagic, macroglossia, and lesions resembling scleroderma.6

Like systemic amyloidosis, localized amyloidosis can be primary or secondary, but this form only affects a single tissue type. It can be deposited either in a diffuse manner or as discrete tumor-like formations.7 Primary localized amyloidosis can affect tissues such as the heart, breast, lung, or urinary tract. Secondary localized amyloidosis can manifest in the cornea (due to inflammatory conditions such as syphilis), the thyroid (due to medullary thyroid cancer), or the skin (due to primary skin tumors).4,8,9

Localized cutaneous amyloidosis affects only the skin and can be subdivided into nodular, macular, lichenoid (papular), or secondary categories. Macular amyloidosis and lichen amyloidosis are thought to be different clinical ...

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