Lichen amyloidosis (LA) is the most common form of primary cutaneous amyloidosis (a category which also includes macular and nodular amyloidosis, poikiloderma-like cutaneous amyloidosis, primary cutaneous amyloidosis of the auricular concha, and the exceedingly rare entity of amyloidosis cutis dyschromica). In LA, a proteinaceous material, amyloid, which is derived from keratinocytes, is deposited in the superficial dermis without involvement of other tissue.

While the cause of LA is incompletely understood, it is associated with, and probably caused by, friction and scratching with fingernails or implements such as towels or brushes.

Clinically, LA manifests as hyperpigmented papules that coalesce to form thick plaques with a "seafloor-like" rippled appearance. The most common location is the pretibial area, but the thighs, forearms, and back can also be involved. LA and macular amyloidosis (MA) are believed to exist on a spectrum and are mainly differentiated by the nature of the primary lesion (papules and plaques in LA and macules and patches in MA) and histopathologic findings. Some patients also display features of both LA and MA, which is termed "biphasic amyloidosis."

LA is intensely pruritic. LA has been reported in association with a few syndromes, particularly multiple endocrine neoplasia type 2A (Sipple syndrome). LA in this syndrome is usually localized to the back in the intrascapular area, and it is histologically and biochemically identical to other forms of keratinocyte-derived LA unassociated with syndromic disease.