Myelomatous pleural effusion: clinical course and immunologic characterization of the pleural fluid cells

Multiple myeloma is a disease that infrequently involves nonreticuloendothelial tissues and rarely causes pleural effusion. A 59-year-old woman had pleural effusion as the major manifestation of multiple myeloma. Light microscopy of her pleural fluid with Wright stained preparations showed all cells to be bizarre and often multinucleated plasmacytes. Electron microscopy confirmed these results. Intracellular immunofluorescence revealed IgG-kappa immunoglobulin (Ig) in greater than 90% of these cells. Surface immunofluorescence using anti-Ig sera was seen on less than 5% of the pleural fluid cells. 3H leucine incorporation into Ig in vitro was measured for these cells, and secretory curves were obtained that have the typical secretory kinetics of bone marrow plasmacytes. This demonstrates that such cells are viable and are able to synthesize and release immunoglobulin. Treatment of our patient with prednisone, melphalan, and cyclophosphamide resulted in symptomatic improvement and complete resolution of her pleural effusion. Pleural effusion is an unusual but important complication of multiple myeloma and does not necessarily carry the grave prognosis implied in previous reports.