There are three myeloid cell lines in the bone marrow: granulocytic, erythroid, and megakaryocytic. The MDS may affect one or more of the myeloid cell lines resulting in anemia, neutropenia, and/or thrombocytopenia.
The anemia caused by MDS is normocytic or macrocytic (non-megaloblastic). The hemoglobin is typically less than 10 g/dL. The reticulocyte count is normal to low and patients are usually transfusion-dependent. The anemia in MDS is refractory to any replacement therapy (iron, B12, or folate).
Neutropenia (decreased neutrophil count) and thrombocytopenia (decreased platelet count) are also observed in MDS. Patients with MDS commonly have neutrophil counts less than 1,800/µL and platelet counts less than 100,000/µL.
Organomegaly (large liver & spleen) is not commonly observed in MDS in contrast to myeloproliferative neoplasm (example: chronic myelogenous leukemia) which is associated with the enlargement of the liver & spleen.
Patients are not diagnosed with MDS without complete knowledge of clinical and drug history. Repeated bone marrow biopsies over a period of several months may be necessary in some cases to establish this diagnosis.