Morphology and Classification of Myelodysplastic Syndromes

Myelodysplastic syndromes (MDS) are a group of hematopoietic neoplasms having ineffective production of one or more cell lines with accompanying morphologic abnormalities in common. This may include notably ringed sideroblasts, megaloblastic erythroid precursors, hypogranulation/hyposegmentation of the granulocytes, and micromegakaryocytes. The percentage of leukemic blasts is variable. Both primary (idiopathic) and secondary (therapy-related) MDS are discussed. The French-American-British (FAB) group classifies MDS into five subgroups. These groups are based on the presence of dysplasia, the number of monocytes, and the percentage of ringed sideroblasts and myeloblasts. Excellent correlation exists between the FAB subgroup and acute leukemic progression/survival. Outcome to a large degree is based on the percentage of blasts at diagnosis, the degree of pancytopenia, and dysplasia.