[Acute megakaryoblastic leukemia developing 11 years after diagnosis of essential thrombocythemia]

A 57-year-old man was diagnosed to have essential thrombocythemia (ET) in July 1977. He was doing well with continual medication of carboquone but was hospitalized because of slight unconsciousness and gait disturbance in May, 1988. His laboratory data were as follows: WBC count 81,600/microliters with 55% of blasts with cytoplasmic blebs, Hb 10.2 g/dl, and platelet count 2.6 x 10(4)/microliters. Bone marrow aspiration revealed hypercellular marrow with 72.8% blasts. Chromosomal analysis showed tetraploidy with 7p+ and 19p+. Cytochemistry of blasts showed the positivity for platelet peroxidase and CDw 41. The diagnosis of acute megakaryoblastic leukemia was made. Meningeal leukemia was also suspected by the cerebrospinal fluid data, and cytarabine was intrathecally injected. Then the percent of blasts of peripheral blood gradually decreased and the data of cerebrospinal fluid improved. However, several days later the patient became comatose probably due to cerebral bleeding, and died. In this case, two possibilities were considered (1) that a blastic transformation to acute leukemia from ET, and (2) that a secondary leukemia developed as a result of the chemotherapy, independently of ET. Since there was no evidence of myelodysplastic syndrome, it was concluded that this case represented a blastic transformation of ET.