Amyloidoses

Amyloidoses are a heterogeneous group of diseases in which a fibrillar proteinaceous insoluble material called amyloid accumulates in various tissues and organs. Amyloid is not a single substance but describes various types of protein aggregations that share the characteristic unifying properties of congophilia and doubly refractile green color under polariscopy, distinctive fibrillar ultrastructure, and a β-pleated sheet structural conformation. Amyloidoses are identified according to the nature of the main amyloid precursor protein and classified into systemic amyloidoses and localized cutaneous amyloidoses. Systemic amyloidoses include primary, secondary, and hereditary/familial forms, while the primary localized cutaneous amyloidoses include three major forms: lichen amyloidosis and macular amyloidosis in which amyloid deposits are due to keratin, and primary nodular cutaneous amyloidosis that occurs as a result of deposition of immunoglobulin light chains produced by a local proliferation of plasma cells. Among the systemic amyloidoses, primary and myeloma-associated systemic amyloidosis is the most common form in which 40% of patients develop mucocutaneous disease, while secondary systemic amyloidoses and hemodialysis-associated amyloidosis present rarely with cutaneous involvement. © 2010 Springer Science+Business Media, LLC.