ITP is thought to be caused primarily by peripheral platelet destruction, but recent work has suggested that platelet production may also be impaired. Although the clinical course in children usually differs from that in adults, no distinctions have been established with regard to marrow characteristics. To evaluate megakaryocyte (mega) responses in this disease we examined mega size, ploidy, maturation and morphology in 8 children and in 8 adults with ITP and in 8 "normal" marrows (4 children, 4 adults). Marrows were prepared by a buffy coat wedge smear or by a cover slip squash method. Control values differed according to the type of marrow smear used. From 100-300 Feulgen-stained megas were examined in each specimen, as previously described. Wright-stained material was also examined. With the squash method megas from normal children and adults had similar characteristics. The megas of each child with acute ITP showed marked increases in size (volumes were 4X normal), ploidy (as high as 1024 N; medians were 64N, or 2 doublings higher than normals), and maturation stage (86% mature forms vs 43%). In contrast, none of the marrows of adults with acute or chronic ITP (1 with mild, 4 moderate, and 3 with severe thrombocytopenias) showed any stimulation of megas. Overall, their megas were normal in size, ploidy and maturation. Occasional dissociation of mega ploidy and maturation was seen, but not enough to alter the profiles of any one parameter. There were no obvious or suggestive signs of "damage" to the megas of children or adults with ITP. In conclusion, the megas of childhood ITP showed a pattern of marked stimulation of size, ploidy and maturation, as seen in animals injected with antiplatelet serum. The failure of adult marrows to response in these parameters to thrombocytopenia may be pathogenetically related to the chronicity of adult ITP.
