Primary localized cutaneous amyloidosis: dermal amyloid deposits do not bind antibodies to amyloid A protein, prealbumin or fibronectin

The chemical nature of the dermal amyloid deposits in primary localized cutaneous amyloidosis (PLCA) was investigated using histochemical and immunohistochemical techniques. Deposits of macular, papular and nodular PLCA showed potassium permanganate resistance of their affinity for Congo red dye, unlike amyloid A protein (AA) deposits, and did not bind antibodies to AA, prealbumin or fibronectin. Despite the frequent presence of immunoglobulins in deposits of macular and papular PLCA, there is no evidence that the amyloid fibrils are composed of protein AL. Although previous studies have identified keratin‐like material in deposits of macular and papular PLCA, the exact nature of the amyloid fibril protein in these conditions, and the mechanism by which tonofilaments of necrotic keratinocytes are trans formed into amyloid material in the papillary dermis, remain uncertain.