ABSTRACT
Dysplastic red cells precursors (dyserythropoiesis) are characterized by nuclear and cytoplasmic abnormalities. Dysplastic nuclear features include asymmetric budding, multinucleation, hyperchromasia, internuclear bridging, megaloblastic changes, and kar yorrhexis. Cytoplasmic abnormalities include dyssynchronous maturation (nuclear-cytoplasmic dyssynchrony), vacuolation, nuclear fragments (basophilic stippling), and ringed sideroblastosis. Although there is usually erythroid hyperplasia, occasional cases of MDS display erythroid hypoplasia. Ringed sideroblasts are defined by at least five iron granules per cell encircling one-third or more of the nuclear rim (normally <4 cytoplasmic ferritin particles can be seen in a subset of erythroid precursors). Dysgranulopoiesis is characterized by hypogranular (agranular) cytoplasm, atypical cytoplasmic granules, pseudo-Pelger-Huet cells (nuclear hypolobation), small or large size, Auer rods, chromatin clumping, ring formation, and irregular hyperseg-mentation. Dysplastic features of megakaryocytes include micromegakaryocytes (“dwarf forms”), hypolobated or large non-lobated nuclei, and multinucleation. The recommended percentage of cells with dysplasia for the diagnosis is ≥ 10%. Increased numbers of blasts, the presence of ringed sideroblasts, micromegakaryocytes, and pseudo-Pelger-Huet cells correlate most strongly with the presence of clonal cytogenetic abnormalities in MDS. The cytomorphologic findings are complemented by histologic features, which include increased number of megakaryocytes, megakaryocytic atypia, abnormal localization of immature precursors (ALIPs), decreased M:E ratio due to erythroid hyperplasia, and/or increased reticulin fibrosis. Histologic analysis is also helpful to exclude other disorders (both hematopoietic and nonhematopoietic) and separate MDS from aplastic anemia.
