Clinical and laboratory features and pathologic findings

PV occurs primarily in older children. In the largest reported series, the median age at presentation was 16 years and included no children younger than 6 years of age [126]. ttere may be a male predominance in pediatric PV. Organomegaly is uncommon. tte frequency of thrombotic events in children with PV appears to be lower than in affected adults. Laboratory studies reveal a significantly increased red cell mass, with a median Hb and Hct of 18gldL and 54%, respectively. tte median WBC and platelet counts are usually within the normal range, although some patients may have mild leukocytosis or marked thrombocytosis, necessitating distinction of PV from other myeloproliferative neoplasms, especially CML and ET. tte serum EPO level is normal in most patients. Evaluation for a positive family history is a critical part of the clinical assessment of an erythrocytotic child. A positive family history, isolated erythrocytosis, and the absence of organomegaly strongly favor a congenital erythrocytosis and make the neoplastic condition PV much less likely. A bone marrow examination may not be indicated in this clinical setting. Finally, such patients and affected famdy members should undergo genetic analysis to assess for the presence of a mutation in EPOR or other relevant genes.

Tte bone marrow findings in pediatric PV are similar to those seen in adults, although there are few reported details of the bone marrow findings in pediatric cases [141]. tte bone marrow is normocellular or hypercellular, usually with trilineage hyperplasia (Fig. 12.17). Erythroid hyperplasia can be pronounced, and myelopoiesis is frequently left-shifted. Significant dysplasia is not present. In addition to hyperplasia, megakaryocytes manifest clustering. A spectrum ofmegakaryocytic morphology, that is, small, intermediate and large, occasionally hyperlobated forms, is typical of PV. In cases with prominent megakaryocytic hyperplasia, distinction from pediatric ET on a morphologic basis alone may be difficult, as large megakaryocytes with hyperlobated nuclei characteristic of adult ET may be less frequent in pediatric cases. Prominent fibrosis has not been described. tte propensity of pediatric PV to progress to spent phase or undergo blastic transformation is unknown.

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