Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android


  • Myelodysplasia or myelodysplastic syndrome (MDS) is the term used, as a generalization, to encompass a diverse group of hematopoietic neoplasms that have in common (1) their origin in a somatically mutated lymphohematopoietic stem cell or a very closely related multipotential hematopoietic cell, (2) late precursor apoptosis (ineffective hematopoiesis) leading to cytopenias despite a normocellular or hypercellular marrow, (3) marrow and blood cell dysmorphology, and (4) a propensity to undergo clonal progression to acute myelogenous leukemia (AML).

  • By definition, dysplasia is a morphologic tissue pathology that is polyclonal, as demonstrated by the distinction between uterine cervical dysplasia (a benign, polyclonal lesion) and uterine cervical carcinoma in situ (a clonal neoplastic lesion). Monoclonality distinguishes neoplasia from all other tissue abnormalities: aplasia (hypoplasia), hyperplasia, metaplasia, and dysplasia. Nevertheless, because dysmorphic neoplastic changes are a critical diagnostic component of its manifestations, the World Health Organization (WHO) has chosen to retain the designation myelodysplasia to highlight the morphologic aberrations observed in neoplastic blood and marrow cells, a critical feature in its diagnosis.

  • The spectrum of clinical disorders ranges from (1) an indolent neoplasm with mild or moderate anemia to (2) more troublesome multicytopenias without morphologic evidence of a large accumulation of leukemic blast cells (≤4% or less) to (3), in effect, subacute myelogenous leukemia with leukemic blast cells in the marrow (range 5%–19%) and blood (range 1%–19%).

  • The manifestations of MDS with cytopenias vary from a single cytopenia (eg, anemia) with a marrow with erythroid dysmorphia to two or three severe cytopenias with hypercellular marrow and with dysmorphia of marrow precursors in each major lineage and of blood neutrophils, red cells, and platelets.

  • This spectrum of expression of the neoplastic transformation is a reflection of the retained ability of the neoplastic hematopoietic stem cell to differentiate, albeit pathologically, into any of 11 lineages, with each lineage capable of maturing into phenocopies of some stage of precursor up to mature cells in each lineage. This matrix provides the resultant wide variation in the phenotype of the disease at presentation. Probably, no two cases are precisely alike phenotypically. Classification cannot encompass this degree of variation. Thus, the physician and scientist have to consider this as we pigeonhole each case as closely as possible into one or another of the categories proposed.

  • Because the neoplasm originates in a multipotential hematopoietic cell (eg, the lymphohematopoietic stem cell), careful inspection of blood and marrow will frequently uncover slight or mild involvement of all three major lineages (eg, low-normal blood cell counts) or subtle morphologic abnormalities in blood or marrow cells.

  • Myelodysplasia with excess blasts (synonyms: oligoblastic or subacute myelogenous leukemia) refers to patients with cytopenias and with a marrow specimen containing 5% to 19% leukemic blast cells. The WHO classification divides this diagnostic category into two types based on the blast counts (5%–9% and 10%–19%).

  • The use of less than 5% marrow blasts as a demarcation between a normal and pathologic blast percentage is an anachronism dating from a decision made ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.