Cutaneous involvement of multiple myeloma and extramedullary plasmacytoma.

We recently performed a retrospective clinicopathologic study of five patients with cutaneous involvement of multiple myeloma or extramedullary plasmacytoma. Cutaneous nodules without extension from an underlying bony focus of disease developed in each case. In two cases skin lesions occurred in the more common setting of advanced disease, but in two others skin lesions provided early clues to the diagnosis. In three patients the appearance of skin lesions heralded a rapidly deteriorating clinical course, but two other patients had reasonably long survivals despite cutaneous disease (6 and 3 years, respectively). Two histopathologic configurations were identified in cutaneous lesions: nodular and infiltrative. Both patients with the latter form had multiple myeloma. In all cases tumor cells were pyroninophilic. Immunoperoxidase studies on fixed, paraffin-embedded tissues confirmed the electrophoretic findings in two cases, but findings were equivocal in three others. In one case, cells were positive for epithelial membrane antigen, and in another, alpha 1-antichymotrypsin-positive cells were observed in the centers of tumor islands. Cutaneous involvement with plasma cell neoplasms is recognized infrequently. Immunohistochemical techniques may prove to be valuable in evaluating these cases, but they are not without technical and interpretative difficulties.