Take Home Point: The diagnosis of AML is made with the presence of at least 20% myeloid blasts in the bone marrow. The number of blasts in the peripheral blood is highly variable.
MDS (myelodysplastic syndrome) refers to a group of clonal stem cell disorders characterized by defects in maturation, associated with ineffective hematopoiesis and high risk of transformation to AML.
Primary MDS is predominantly a disease of the elderly (mean age of onset is 70), and consists of 5 subtypes. Subtypes that have a higher proportion of blasts are associated with more severe cytopenias, an increased risk of progression to AML, and a worse prognosis. Progression to AML occurs in 10-40% of patients.
MDS-related AML is easily diagnosed in the setting of a well-documented history of MDS or myeloproliferative disorder that has been present for over 6 months. In cases that present initially as AML, the identification of MDS-related disease is more complicated.
The diagnosis of AML is made with the presence of at least 20% myeloid blasts in the bone marrow. The number of blasts in the peripheral blood is highly variable. There are less than 10,000 blasts per mm^3 in the peripheral blood in over 50% of AML patients. In some cases of AML, one will find no blasts in the peripheral blood! For this reason, a bone marrow biopsy is required to exclude leukemia in patients with pancytopenia.
Kumar et al. (2010). Diseases of the White Blood Cells, Lymph Nodes, Spleen, and Thymus. In Robbins and Cotran (Eds.) Pathologic Basis of Disease (620-625). Philadelphia, PA: Saunders-Elsevier.