RESUMO
UNLABELLED: Authors present a case of a therapy-resistant multiple myeloma who developed plasmacytic skin infiltration in the course of the disease. AIM: To define characteristics of skin infiltrating plasma cells, which differentiate them from those cells residing in the bone marrow in order to contribute to a better understanding of the epidermoinvasion process. METHODS: Histidine decarboxylase is the only enzyme capable for histamine synthesis having significance in cell proliferation. Histidine decarboxylase was determined in skin samples and bone marrow slides by immunohistochemical procedures and in bone marrow cells using flow cytometry analysis. RESULTS: The histidine decarboxylase expression of plasma cells participating in skin invasion disappeared, while that of bone marrow plasma cells remained. CONCLUSIONS: Authors conclude that the histidine decarboxylase loss would serve as an evidence for the dedifferentiation of epidermoinvasive cells as being the result of fundamental changes in histamine metabolism. As extramedullary myeloma cells differ from those residing in the bone marrow, their therapeutical response might also be different.