Myelofibrosis Developing in Megakaryoblastic Leukemia in a Boy with Down's Syndrome

A 2 1 /2-year-old boy with Down's syndrome developed pancytopenia. After spontaneous recovery, leukocytosis with blast cells in peripheral blood and bone marrow developed, and it was associated with thrombocytopenia and splenomegaly. After transient but complete disappearance of all of these findings, they reappeared and a marked fluctuation with 4 subsequent peaks of leukocytosis was observed. Splenomegaly appeared in association with eukocytosis in early phase and persisted after the third peak. Blast cells were identified as megakaryoblasts and had a karyotype of 47, XY, -7, -1 2, +21, +der(7)t(7p+;?)(p22;?), +der(12)t(6;12p+)(pll;ll). Bone marrow biopsy at the time of recovery from pancytopenia showed hypercellularity with many megakaryocytes and minimal fibrosis. Subsequent serial bone marrow biopsies showed progressively developing fibrosis leading to the final picture of typical myelofibrosis. A histological examination of spleen and an omental tissue showed marked blastic infiltration associated with megakaryocytic infiltration. This case suggests that megakaryoblastic leukemia associated with myelofibrosis is anadditional type of abnormal myelopoiesis seen in Down's syndrome.