Plasma cell dyscrasias are characterized by neoplastic proliferation of a single clone of plasma cells typically producing a monoclonal immunoglobulin. Plasma cell neoplasms can present as a single lesion (solitary plasmacytoma) or more commonly as multiple lesions (multiple myeloma). Plasmacytomas can be present at the initial diagnosis of multiple myeloma or develop later during the course of the disease.
When plasmacytoma is associated with 10 percent or more clonal plasma cells in the bone marrow, the diagnosis is considered to be multiple myeloma rather than solitary plasmacytoma. While solitary plasmacytomas are treated with radiotherapy, multiple myeloma is treated with chemotherapy.