Definition of Myelodysplastic syndrome
Myelodysplastic syndrome: A group of bone marrow disorders characterized by the underproduction of one or more types of blood cells due to dysfuntion of the marrow. The myelodysplastic syndromes (MDS) may arise de novo (newly) or be secondary to treatment with chemotherapy or radiation therapy for another disease. De novo myelodysplasia usually has a better prognosis than does secondary myelodysplasia.
MDS is characterized by low red blood cells (anemia), low white blood cell count (leukopenia) with a tendency to infection, and low platelet count (thrombocytopenia) with bleeding problems. MDS may progress and transform into acute myelogenous leukemia (AML).
The 7 recognized types of MDS are refractory anemia, refractory anemia with ringed sideroblasts, refractory anemia with excess blasts, refractory anemia with excess blasts in transformation, chronic myelomonocytic leukemia, chronic myelomonocytic leukemia in transformation, and unclassified myelodysplastic syndrome.
The survival rates range from six months to a number of years for the different subtypes of MDS. Death is usually due to bleeding or infection. Transformation to AML occurs in up to 40% of patients and carries a poor prognosis.
Supportive care has traditionally been the mainstay of treatment. This includes the judicious use of platelet and blood transfusions. Vidaza (azacitidine) is the first drug approved (in 2004) for treating MDS. It causes demethylation or hypomethylation of DNA in abnormal blood-forming (hematopoietic) cells in the marrow and also has a direct cytotoxic effect.
The highest prevalence of MDS is in people over 60 years of age. About 10,000 to 30,000 new cases of MDS are diagnosed annually in the US.
Last Editorial Review: 5/20/2004Common Misspellings: myelodysplastic syndrone
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