Abstract
A ten-year-old boy with myelodysplastic syndrome was presented. Pancytopenia associated with erythroid and myeloid dysplasia such as a Pelger-Hüet-like anomaly was observed. Giant platelets were also noted. Chromosome analysis revealed an abnormal 45XY, -7 (monosomy 7) pattern. Throughout the clinical course, a remarkable proliferation of monocytoid cells were exhibited. Flow cytometric analysis revealed that these cells were identified in the same cytographic region as that of normal monocytes. However, these proliferative monocytoid cells were negative for naphthyl butylate esterase stain, and were positive for peroxidase and naphthol AS-D chloroacetate esterase stain. In addition, immunologic surface marker analysis using monoclonal antibodies revealed that the monocytoid cells had an OKM1 antigen, but did not have OKM5 or Leu M2 antigens at all which were considered to be the monocyte-specific antigens. In spite of aggressive chemotherapies and supportive care, 32 months after diagnosis the patient died of interstitial pneumonia through a partial transformation to chronic myelomonocytic leukemia. This is the first report in which the OKM1 +/OKM5-monocytoid cells are identified although the precise role of these cells in the childhood preleukemic stage remains to be elucidated.
