Malignant Hematolymphoid Plasmacytic Effusions: A Cytopathologic Study of Six Cases.

Compared to myelomatous effusions, there is a lack of studies that specifically address hematolymphoid plasmacytic effusions (HPEs). We conducted a retrospective review study over 15 years to investigate the prevalence, cytologic patterns, potential interpretation pitfalls, and clinical associations of HPEs. Serous effusion fluids in which plasmacytoid and plasma cells represented more than 10% of effusion cells were classified as HPEs. We extracted relevant clinical, laboratory, and follow-up data for each patient. We found six patients [age range: 60-88, average age: 73, male to female ratio 1:1] with HPEs that constituted 0.2% of serous effusions. Relevant clinical history prompted us to consider HPEs and include plasma cell immunomarkers in cellblock sections. Light chain-restricted plasmacytic cellular infiltrates confirmed the cytologic diagnosis in the absence of fluid flow cytometry. We have recognized three cytomorphologic patterns: pure plasmacytic infiltrates, lymphoplasmacytic infiltrates, and plasma cells intermixed with other cellular constituents. Four patients had multiple myeloma (two patients with pure high-grade large pleomorphic myeloma cells, two patients with mature plasma cells intermixed with inflammatory cells), one patient had marginal zone lymphoma, and another patient had lymphoplasmacytic lymphoma. The patients had similar clinical features with even kappa (3 cases) and lambda (3 cases) light chain distribution. HPEs are uncommon malignant effusions that occur in elderly patients with multiple myeloma and low-grade B-cell lymphomas. High-grade myeloma cells can be confused with hematolymphoid and non-hematolymphoid malignancies, whereas mature plasma cells in multiple myeloma and low-grade lymphomas can be misinterpreted as reactive plasmacytosis. Cellblock immunocytochemistry is a valuable diagnostic tool.