The platelets in preleukemia and myelomonocytic leukemia. Ultrastructural cytochemistry and cytogenetics.

Light and electron microscopic studies of platelets from 16 patients with myelomonocytic leukemia or "preleukemia" revealed major morphologic alterations in 15 and minor ones in 1. Although variable in severity from case to case, the changes present followed a distinct pattern. In most cases there were two platelet populations, one morphologically normal and one morpholigically abnormal. The most salient changes pertained to size (giant forms), shape (the platelets being rounded and probably spheroidal), decrease or absence of the microtubules, and increase in immature elements. A striking feature was the variation in size and shape of the granules, with truly giant forms (up to 2.5 mum) being present. In cytogenetic studies in 14 cases, there was no correlation between the chromosomal changes and the various types of platelet anomalies.