Primary systemic amyloidosis, usually with an underlying plasma cell dyscrasia, is associated with a wide spectrum of organ involvement. Skin infiltration by amyloid presents as waxy, translucent, or purpuric papules, nodules, and plaques. Petechiae, purpura, and ecchymosis often are observed, especially on the eyelids, due to infiltration of vessel walls. Histopathology is characterized by amorphous material in the dermis and subcutaneous tissue. Amyloid often is found around adnexal structures and within blood vessel walls, staining pink with hematoxylin and eosin and metachromatic with crystal violet and methyl violet. Amyloid stained by Congo red gives an apple green birefringence when viewed under polarized light.
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