Myelodysplastic syndrome (MDS) refers to a heterogeneous group of closely related clonal hematopoietic disorders. All are characterized by a hypercellular or hypocellular marrow with impaired morphology and maturation and peripheral blood cytopenias, resulting from ineffective blood cell production. All 3 cell lineages in myeloid hematopoiesis can be involved, including erythrocytic, granulocytic, and megakaryocytic cell lines. Although clonal, MDS is considered a premalignant condition in a subgroup of patients that often progresses to acute myelogenous leukemia when additional genetic abnormalities are acquired.

Patients with MDS may present with clinical manifestations of anemia, thrombocytopenia, and/or neutropenia (see Clinical). The workup in patients with possible MDS includes a complete blood count with differential, peripheral blood smear, and bone marrow studies.