BACKGROUND: Essential thrombocythemia(ET) is a rare chronic myeloproliferative disorder characterized by an extremely high platelet count in the circulating blood and abnormal proliferation of the megakaryocytes in bone marrow, resulting in splenomegaly, thromboembolic or hemorrhagic complications. We studied the presence of nuclear hyperploidy of the megakaryocytes in bone marrow, the presence of abnormal response to the individual reagent on platelet aggregation test, and its clinical implication.
METHODS: We analyzed the 43 cases of ET at the Asan Medical Center between January, 1989 and March, 1999. The Polycythemia Vera Study Group criteria were used to diagnose ET.
RESULTS: Nuclear hyperploidy was observed at 43 cases (100%). Platelet aggregation test was done at 32 (74.4%) cases, of which 27 (84.4%) cases showed abnormal response to more than one reagent, 16(50%) cases to more than two reagents. Abnormal response to epinephrine and collagen was most common, but 5 cases showed normal response. By individual reagent, 1 (3%) cases to adenosine diphosphate, 1 (3%) case to ristocetin, 22 (69%) cases to epinephrine, 19 (59%) cases to collagen showed abnormal response.
CONCLUSION: We observe that nuclear hyperploidy of the
megakaryocyts and abnormal response on platelet aggregation test are frequent in ET in this study.

Keywords: Platelet aggregation test, Essential thrombocythemia, Nuclear hyperploidy