What does myeloproliferative disorder with essential thrombocythemia mean?

Too many platelets: The myeloproliferative neoplasms (mpns) involve terminal myeloid cell expansion in the peripheral blood, resulting in various combinations of erythrocytosis (rbc's), leukocytosis (wbc's), thrombocytosis (platelets), bone marrow hypercellularity/fibrosis, and splenomegaly (enlarged spleen). Essential thrombocythemia is a diagnosis of exclusion, made when other forms of mpn are ruled out.