A basic classification and a comprehensive examination of pediatric myeloproliferative syndromes

Myeloproliferative syndromes (MPSs) are clonal stem cell disorders resulting in excessive proliferation of one or more cell lineages. Since MPSs in children occur much less commonly than adults, one can argue that the biology and the categories of the various pediatric MPSs seem to be different from adults. Furthermore, confusion exists between pediatric MPS and other overlapping conditions, such as myelodysplastic syndrome. The authors' objectives were to develop a classification system with a list of disorders relevant to children and to characterize pediatric cases of MPS that were devised according to this classification. Based on the predominant proliferating cell lineage, the authors established a classification system for childhood MPS. Primary MPS was classified into granulocytic proliferation--chronic myelogenous leukemia (CML); monocytic--juvenile myelomonocytic leukemia (JMML); megakaryocytic--essential thrombocythemia (ET), familial thrombocytosis, transient myeloproliferative disorder of Down syndrome (TMD); erythrocytic--polycythemia vera, familial erythrocytosis; fibroblastic--idiopathic myelofibrosis (IMF); eosinophilic--idiopathic hypereosinophilic syndrome (IHES); and mast cells--mastocytosis. Secondary MPS was classified as non-clonal proliferation (eg, infections, drugs, toxins, autoimmune, non-hematologic neoplasm, and trauma), and these were excluded from the study. Next, the classification system was applied to the patient population at the authors' institution. One hundred two cases with primary MPS were identified between 1970 and 2001. Patients were evaluated for clinical manifestations, blood and bone marrow parameters, cytogenetics, and survival following different treatment modalities. Significant proportions of cases of childhood MPS (60%) were unique to the pediatric population and not seen in adults. The most common disorders were JMML (n = 31), TMD of Down syndrome (n = 30), and CML (n = 30); the other disorders were rare: four cases of ET, two of IMF, two of IHES, two of mastocytosis, and one primary erythrocytosis. In contrast to adults, MPS in children is more frequently treated with hematopoietic stem cell transplantation (HSCT), the only available curative option for most of these diseases. HSCT was particularly successful in the more recent cases due to more advanced techniques for HSCT. The authors found that all the cases could be easily classified. MPS in children is different from adult-type MPS in terms of biology, categories, classification, and prognosis.