Pseudoleukemia. Ineffective regulation of granulopoiesis

A neonate with Down's syndrome confirmed by chromosomal analysis had leukocytosis, with a WBC count of 48,000/cu mm, at age 13 days. Differential counts showed 70% to 90% blast forms by light microscopy. The blast-cell granules stained negatively with Sudan black B and alpha-napthyl butyrate esterase. Myeloperoxidase activity evaluated light and electron microscopy was negative. The granules stained positively with PAS, beta-glucuronidase, and tartrate-sensitive acid phosphatase. Indirect immunofluorescence for terminal-deoxynucleotidyl-transferase was negative. Our results show that the blast cells of pseudoleukemia may be of lymphoid origin.