Myelomatous pleural effusion.

Malignant pleural effusions due to multiple myeloma are rare. Effusion in such patients is usually due to congestive heart failure or another process. Malignant myeloma cells identified in cytologic examination of the pleural fluid or by pleural biopsy establish the diagnosis of a myelomatous effusion. This finding portends a poor prognosis and death usually within 4 months.