Nodular localized cutaneous amyloidosis: detection of monoclonality of infiltrating plasma cells by polymerase chain reaction.

We report nodular localized cutaneous amyloidosis arising in a 74-year-old woman as a single nodule at the left angle of the mouth. Histological examination revealed eosinophilic material deposited in the dermis, identified as amyloid by staining with Dylon stain, and antiamyloid P component, and by electron microscopy. The amyloid material was further determined immunohistochemically to be of AL fibril protein type derived from lambda light chains. Infiltrating plasma cells, around blood vessels in the dermis, stained monotypically with anti-lambda antibody, suggesting plasma cell monoclonality. Semi-nested polymerase chain reaction (PCR), for rearrangement of immunoglobulin heavy chain gene using paraffin-embedded sections, yielded two distinct amplified bands, indicating monoclonality of the infiltrating plasma cells. These findings support the hypothesis that primary localized nodular amyloidosis involves local accumulation of monoclonal plasma cells and their secreted products. The two amplified bands observed on PCR may, in the present case, reflect abnormal secretion of immunoglobulin light chains.