Myeloma with involvement of the serous cavities. Cytologic and immunochemical diagnosis and literature review.

The significance of serous cavity involvement by myeloma was evaluated in two patients with pleural involvement and two with peritoneal involvement. The involvement occurred at presentation in two patients and after the diagnosis of myeloma in two. The effusions were bloody exudates containing numerous atypical plasma cells. The diagnosis of cavitary involvement was made by morphologic examination of air-dried smears of the effusions, supplemented by the immunocytochemical demonstration of monoclonal proliferation of the plasma cells. In all four cases, these cells contained cytoplasmic kappa light chain immunoglobulins; many of them also stained positively for epithelial membrane antigen. It was best to interpret these immunocytochemical findings with those of the morphologic and additional immunocytochemical studies; the best results for studies for cytoplasmic immunoglobulins were obtained only if the cells in the effusions were washed before they were used for smear preparations and staining. The four patients responded poorly to treatment, dying 12 days, 16 months, 1 month and 10 days after cavitary involvement was recognized. Review of the literature confirmed that the findings in these cases were similar to those in other cases. Cavitary involvement by myeloma carries an ominous prognosis; an accurate recognition of the plasma cells by morphologic and immunocytochemical studies provides the best method of diagnosing cavitary involvement of myeloma and of predicting the poor outcome in such patients.