Localized oral amyloidosis: ultrastructural and immunohistochemical study.

An histopathological, ultrastructural and immunohistochemical study of localized amyloidosis in the floor of mouth of a 58-year-old male in good health is reported. The lesion was composed of nodular deposits of amyloid surrounded by fibroblastic or histiocytic cells, and metaplastic ossification was seen in some deposits. Ultrastructural findings disclosed typical amyloid fibrils with felt-like structure. Closely connected with the amyloid deposits were cells with active histiocytic or fibroblastic appearance. Their cytoplasm contained amyloid fibrils. At the outermost area of the amyloid deposits, bundles of amyloid fibrils projected from these cells into amyloid deposits. Amyloid protein of the present case did not react to any antisera using anti-AA, anti-A lambda, anti-A kappa and anti-prealbumin antisera. It can be assumed that histiocytes or fibroblasts play an important role in local amyloid formation, however, the nature of amyloid fibril protein in the present case is unknown.