[Study on pathophysiology of the myelodysplastic syndromes (MDS)--pattern of dysmegakaryopoiesis related to leukemic transformation].

A series of 116 patients with MDS consisted of 74 cases of RA, 10 cases of RARS, 14 cases of RAEB, 9 cases of RAEB-T and 9 cases of CMML, were studied on the quantity and morphological abnormalities of megakaryocytes in relation to over all survival and leukemic change. The amount of megakaryocytes was graded into four groups; marked hypoplasia (O), moderate hypoplasia (L), normoplasia (N) and hyperplasia (H), RA cases showed heterogeneous pattern; containing 14 cases (18.9%) of group (O), 18 cases (24.3%) of group (L), 31 cases (41.9%) of group (N) and 11 cases (14.9%) of group (H). RARS, RAEB, RAEB-T and CMML cases were classified into group (N) or group (H). The heterogeneous pattern of RA did not relate to leukemic change, but over all survival tended to be shorter in group (N) cases. A significant number of young female cases of RA were involved in group (O). Morphological abnormalities of MDS megakaryocytes were classified into five types; I, mononuclear micromegakaryocytes, II, binuclear micromegakaryocytes, III, mononuclear small megakaryocytes, IV, multiseparated-nuclear megakaryocytes and V, megakaryocytes with bizzare nuclei. RAEB and RAEB-T cases uniformly showed marked dysmegakaryopoiesis ranging from type I to V. whereas RA, RARS and CMML cases showed mild dysmegakaryopoiesis. Only five cases (6.4%) of RA cases had type I micromegakaryocytes. Eight RA cases with type I on diagnosis or obtaining it during the clinical course tended to develop acute myeloid leukemia (5 cases) or to transform to RAEB sooner or later. In two cases of RAEB in which hematological improvement was obtained with low dose cytosine arabinoside regimen, disappearance of type I micromegakaryocytes was noted. A female case with 5q-anomaly surviving more than 10 years showed marked megakaryocyte hyperplasia and almost exclusively type III and IV megakaryocytes. These findings indicated that pattern of dysmegakaryopoiesis, especially appearance of type I, was closely related to leukemic change in MDS. Thus quantitative and qualitative evaluations of MDS megakaryocytopoiesis seemed important to understand the further heterogeneity of pathophysiology in MDS subtypes.