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Ballooning platelets in the myelodysplastic syndromes (MDS)

To the Editor: Large, bizarre platelets in peripheral blood of patients with preleukemic syndrome were previously reported (1). In a single earlier study by Widell and Hast in 1987 (2) a distinct subpopulation of platelets in myelodysplastic syndrome (MDS) is described, which by phase contrast microscopic examination has a balloon-shaped bulge of the cell membrane. Increased numbers of such platelets were found in 89% of MDS patients. Among patients with other hematological disorders, 27 % had atypical platelets. In that group, atypical platelets seemed to be associated with recent chemotherapy. It was concluded that an increased number of balloon-like platelets in a cytopenic patient would suggest a diagnosis of MDS, unless associated with recent cytotoxic therapy. We found it of interest to try to reproduce these findings, since they might contribute to the MDS diagnosis. Furthermore we wanted to simplify the blood sampling procedure, thereby making the test more available in routine use. We have studied 14 patients with a diagnosis of MDS. 3 patients were FAB-classified as refractory anemia (RA), 4 as ringsideroblast anemia (RSA), 5 as RA with excess of blasts (RAEB) and 2 as RAEB in transformation (RAEB-t). Most patients were untreated; however, 2 of the RAEB cases had been given low-dose AraC prior to the examination. 12 patients with benign and malignant blood disorders served as diseased controls. None of these had received chemotherapy at the time of the study. 14 healthy volunteers served as healthy controls. Platelet morphology was studied in a Zeiss microscope, using a 40 x phase contrast objective and a 0.05 mm Thoma chamber. Capillary blood (20 PI) was drawn from the ear lobe and immediately diluted 20 x in Kristenson’s solution (urea 10 g, sodium citrate 2.5 g, mercury chloride 0.005 gin 500 ml of aqua dest.; pH 9.0). For comparison, blood samples were drawn from a cubital vein into an EDTA-containing Monovette-system. These samples were afterwards diluted 20 x in Kristenson’s medium and studied as already described. All samples were counted by the same investigator in a blinded manner. A minimum of 200 platelets was evaluated. However, in case of severe thrombocytopenia only 100 platelets were counted these counts were then repeated. In the present study we also were able to demonstrate large, atypical platelets with a balloonor earshaped bulge of the cell membrane in MDS patients using phase contrast microscopic examination. Examples of the atypical platelets in MDS, as seen by phase contrast microscopy, are shown in Figs. lab. The atypical platelets are larger than normal platelets and have a balloonor ear-shaped bulge of the cell membrane. This bulge does not seem to contain any organelles. Depending on the projection, many different shapes can be seen. The atypical platelets are easily distinguished from normal platelets (Fig. 1) and also from macroplatelets seen in ITP. Macroplatelets can be as large but lack the ear-shaped protrusion of the cell membrane and have a more homogeneous appearance. The result of the platelet count is shown in Fig. 2. The count of balloon-like platelets in the MDS group differed significantly from the two other groups (p = 0.001 using a Kruskal-Wallis test). The count of balloon-like platelets in MDS also was significantly higher than in the group with other hematological disorders (p = 0.016 using a MannWhitney test). Comparison between the method using capillary blood immediately diluted in Kristenson’s medium and the method using venous blood in an EDTA-containing Monovette system, which was afterwards diluted in Kristenson’s medium, showed no significant difference (p=0.24 using a Wilcoxon signed-rank test). The count of atypical platelets tended to be slightly, but insignificantly, higher in the EDTA-containing samples. We conclude that closed EDTA blood containers may be used as well. This finding simplifies the test procedure, making it convenient for routine use. Abnormal platelets in low counts were also found among patients with other hematological disorders and even among the healthy controls. We observed