Light chain restriction analysis of bone marrow plasma cells in patients with MGUS or 'solitary' plasmacytoma: diagnostic value and correlation with clinical course.

Twenty-eight patients with a diagnosis of 'solitary' plasmacytoma or with gammopathy but with nondiagnostic morphologic examination of the bone marrow were investigated using a short-term bone marrow culture technique which enriched for the plasma cell fraction. The percentage of monotypic plasma cells in these plasma cell enriched cultures was correlated with the subsequent clinical course. The majority of patients with plasmacytoma and a significant number of those with gammopathy but with otherwise non-diagnostic investigations were found to have a monoclonal plasma cell component of greater than 20%. There was a significant correlation between the percentage of monoclonal plasma cells as detected by bone marrow culture and subsequent progression to disseminated myeloma. These results indicate that early bone marrow involvement can be detected by means of plasma cell culture prior to morphologic identification of marrow plasmacytosis and that short-term plasma cell culture distinguishes patients with early, low bulk myeloma from those with monoclonal gammopathy of uncertain significance (MGUS).