Amyloidosis in the Skin

Amyloidosis is induced by deposition of amyloid proteins in various organs. Both systemic and localized type amyloidosis present with a variety of skin manifestations. Based on biochemical and immunological aspects, amyloid proteins are subdivided into several subtypes from different origins. Amyloid fibrils in primary and multiple myelomaassociated systemic amyloidosis are composed of immunoglobulin protein AL (light chain), whereas in secondary systemic amyloidosis, they are composed of a non-immunoglobulin protein (amyloid AA). In primary localized cutaneous amyloidosis, amyloid materials are derived from cytokeratin; however, in nodular primary cutaneous amyloidosis, amyloid is AL type. Dialysis-related amyloidosis is composed of β2-microglobulin. So far, there are several reviews of skin features associated with amyloidosis [1-3]. Cutaneous amyloidosis is characterized by deposition of amyloid in the skin, which is seen in association with systemic amyloidosis and also restricted to the skin. In case of association with systemic amyloidosis, skin lesions are important as one of the extrahematologic manifestations, because cutaneous lesions may occasionally be the initial presentation of systemic amyloidosis. Representative lesions include petechiae, purpura, ecchymoses, and eyelid translucent papulonodular lesions. By contrast, amyloidosis limited to the skin is called primary localized cutaneous amyloidosis, which is clinically classified into more common macular, papular, and the rare nodular form. Also, reports of cases showing peculiar forms of cutaneous amyloidosis are seen, depending on the different races. Additionally, amyloid deposition is secondarily seen in association with skin tumors, such as basal cell carcinoma, Bowen’s disease, and other benign tumors. In this review, both primary and secondary skin lesions associated with systemic as well as cutaneous amyloidosis are discussed, making a focus on mucocutaneous manifestations.