Essential thrombocythemia in childhood.

In addition to the criteria of the Polycythemia Vera Study Group, positive markers for essential thrombocythemia (ET) include spontaneous BFU-E, splenomegaly, and megakaryocyte morphology in bone marrow smears and biopsy material. The hematologic features of 11 reported cases of ET in childhood showed platelet counts in excess of 1000 x 10(9)/L in all, slight leukocytosis in 8, and splenomegaly in 9. The presenting thrombohemorrhagic manifestations in 8 symptomatic cases were microcirculatory disturbances and transient neurologic ischemic attacks in 2, recurrent mucocutaneous bleedings in 6, and priapism in 1. There are no reports of ET in childhood complicated by microcirculatory disturbances at platelet counts below 1000 x 10(9)/L. Anagrelide and alpha-interferon, which are non-leukemogenic agents for the reduction of platelet counts, may become the treatment of choice in childhood ET. Anagrelide is tolerated better than alpha-interferon. The potential leukemogenic drugs hydroxyurea and busulfan should be used cautiously and withheld as long as possible.