Background: Essential thrombocythemia(ET) is a chronic myeloproliferative clonal disorder characterized by a sustained proliferation of megakaryocytes, which leads to
increased numbers of circulating platelets. The typical presentations of ET are profound megakaryocyte hyperplasia, splenomegaly, and a clinical course punctuated by
hemorrhagic and/or thrombotic episodes. In order to evaluate difference of clinical manifestations, clinical course and therapeutic response, this study was done.
Methods: We analyzed the seven cases of ET at the Yeungnam University Hospital between July, 1982 and July, 1993. The PVSG criteria was used to diagnose ET.
Results: The average age at diagnosis was 57 years(range,46 to 69 years). There were 4 females and 3 males. At diagnosis, 6 patients presented with thromboembolic
complications, and 1 patient with hemorrhage. The hemoglobin level was less than 13gm/dL in 6 cases and platelet aggregation studies were revealed impaired aggregation in response to epinephrine in all cases. Initial bone marrow studies revealed marked megakaryocytic hyperplasia, presence of iron and absence of collagen fibrosis in all cases. Philadelphia chromosome was negative in 5 cases studied. Hydroxyurea was quite efficient to achieve complete response in 5 cases. Median follow-up duration was 12 months(2 months - 72 months) and 6 cases are alive until now. Hemorrhage and thromboembolic episodes have not recurred during follow-up periods in 6 cases.
Conclusion: Major manifestations of ET were thrombosis in this study. Platelet count, thrombotic and hemorrhagic complication of ET were effectively controlled by hydroxyurea.

Keywords: Essential thrombocythemia, Hydroxyurea,