Cytology and flow cytometry of malignant effusions of multiple myeloma

Identifying malignant plasma cells in body fluids from multiple myeloma patients is important for therapeutic and prognostic considerations. This can be difficult when plasma cells are mature in appearance or low in number. We examined the cytological and flow cytometric findings of myelomatous pleural and pericardial effusions from 8 patients with advanced multiple myeloma. Cytoplasmic immunoglobulin light chain excess vs. DNA ploidy in the plasma-cell population was evaluated by flow cytometry (FCM). The cytology smears of one pericardial and 14 pleural effusions from the 8 patients were reviewed. Screening Papanicolaou-stained smears facilitated the detection of malignant nuclear features; however, morphology of plasma cells was best seen in Diff-Quik-stained smears. Low cellularity and inadequate air-drying of smears accounted for the false-negative cytology seen in two fluids from a single patient. A malignant plasma cell population was identified in 9 of 10 fluids submitted for FCM, including the two fluids with negative cytology. The false-negative FCM was from a suboptimal specimen with high background staining. Six fluids had an aneuploid DNA content, and four were diploid. A combination of Papanicolaou- and Diff-Quik-stained smears is recommended for the evaluation of plasma cells in effusions from patients with multiple myeloma. Cytology and flow cytometry confirmed malignancy in 87% and 90% of fluids evaluated, respectively; all cases were diagnosed by either one or both methods. Our results suggest that FCM and cytology of serous effusions in multiple myeloma patients are complementary and should be used in difficult cases. Diagn. Cytopathol. 2000;22:147-151.