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What Are Myelodysplastic Syndromes (MDS)?

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Updated January 26, 2012

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Myelodysplastic syndromes (MDS) are a group of bone marrow diseases that have an increased risk of developing into acute myelogenous leukemia (AML). While these diseases may all have different symptoms and treatments, the one thing that they all have in common is that they effect how much and how well the bone marrow is able to produce healthy blood cells.

Other words that are used to describe MDS are preleukemia, hematopoietic dysplasia, subacute myeloid leukemia, oligoblastic leukemia, or smoldering leukemia.

How Does MDS Develop?

MDS begins with DNA damage or mutation in a single blood forming (hematopoietic) stem cell. As a result of this damage, the bone marrow starts to overproduce blood cells and gets packed with immature or “blast” cells.

In MDS, there is also an increase in programmed cell death (apoptosis), which leads to an interesting paradox. While there may be increased production of cells in the marrow, they do not live long enough to be released out into the blood. Therefore, people with MDS will often suffer from anemia, thrombocytopenia, and neutropenia.

A Pre Leukemia?

Measurement of the number of blast cells in the marrow indicates how severe the disease is - the more immature cells, the more severe. Once your marrow shows that its population is made up of more than 20% blast cells, the condition is considered to be AML.

About 30% of cases of MDS progress to AML. However, it is important to note that even if this transformation never occurs, the anemia, thrombocytopenia and neutropenia associated with MDS is still life threatening.

Subtypes of MDS

Not only does an MDS diagnosis encompass several different bone marrow disorders, there are a number of factors within each of these conditions that determine the behavior and prognosis of the disease. As a result, scientists have struggled to come up with a classification system that takes into account all these different variables.

The first of these systems is the French- American- British (FAB) classification. It breaks MDS down into 5 subtypes based on how the bone marrow looks and the results of the patient’s complete blood count (CBC):

  • Refractory anemia (RA)
  • Refractory anemia with ringed sideroblasts (RARS)
  • Refractory anemia with excess blasts (RAEB)
  • Refractory anemia with excess blasts in transformation (RAEB-T)
  • Chronic monomyelocytic leukemia (CMML)

Since the development of the FAB criteria in 1982, scientists have learned more about the genetic abnormalities that lead to MDS and the role that these mutations play in the course of the disease. As a result, in 2001, the World Health Organization (WHO) published some changes to the FAB system. They added some conditions -- 5q- syndrome, MDS unclassifiable (MDS-U), and refractory cytopenia with multilineage dysplasia (RCMD) -- and subdivided others such as RAEB and CMML based on the percentage of blasts in the bone marrow. They also clarified that anything greater than 20% of blasts in the marrow constituted AML, making RAEB-T a leukemia as opposed to an MDS.

The third method of classifying MDS is using the International Prognostic Scoring System (IPSS). This system uses three criteria for determining how MDS will progress: the number of cells in the patient’s circulating blood, the number of immature blast cells in the bone marrow, and cytogenetics (the type of genetic abnormalities associated with the MDS).

Based on these factors, IPSS divides patients into four categories which indicate the “risk” of the MDS- low, intermediate-1, intermediate-2, and high. The IPSS provides an improved way to predict outcomes of MDS, determine a prognosis, and plan treatment.

Primary vs. Secondary MDS

In most patients, MDS seems to develop for no known reason, out of the blue. This is called primary or de novo MDS. As in the case of leukemia and other bone marrow disorders, scientists are not exactly sure what causes primary MDS.

Secondary MDS refers to the condition when it follows previous treatment with chemotherapy or radiation therapy.

How Is MDS Diagnosed?

MDS is diagnosed using the same techniques used to diagnose leukemia.

The first step is to test the patient’s circulating blood for a complete blood count (CBC). This test looks at the number of healthy red blood cells, white blood cells, and platelets in the blood to get a general idea of what is going on in the marrow. In most cases, a person with MDS will show low numbers of red blood cells (anemia), and possibly low platelets (thrombocytopenia) and neutrophils (neutropenia) as well.

If no other cause can be found for the patient to have anemia, doctors will then perform a bone marrow aspirate and biopsy. In a patient with MDS, the marrow will show an abnormal appearance as well as an increased number of immature or “blast” cells. When the cells are examined at a genetic level, they will show mutations or changes to the chromosomes.

Signs and Symptoms of MDS

Patients with MDS may experience symptoms of anemia such as:

  • Shortness of breath with little exertion
  • Pale skin
  • Feeling tired
  • Chest pain
  • Dizziness

A few patients will also have signs of neutropenia and thrombocytopenia as well, including bleeding problems and difficulty fighting off infections.

It is important to note that there are many other, less serious conditions that can cause these signs and symptoms. If you are worried about any health concerns you are experiencing, it is always best to discuss them with your doctor or other medical professional.

Summing it Up

MDS is not one disease, rather a group of conditions that cause changes to how the bone marrow functions.

As science learns more about genetics and the role they play in the development of these kinds of diseases, we are also learning more about factors that determine the course they will take and the potential outcomes. In the future, researchers will be able to use this information to create new and more effective therapies for MDS.

Sources

Goldberg,S., Chen, E., Corral, M., et al. “Incidence and Clinical Complications of Myelodysplastic Syndromes Among United States Medicare Beneficiaries” Journal of Clinical Oncology June 2010. 28: 2847-2852.

Bowen, D. “Management of Patients with Myelodysplastic Syndromes: Introductory Concepts” in Deeg, H., Bowen, D., Gore, S., Haferlach, T., Beau, M., Niemeyer, C. (eds) (2006) Hematologic Malignancies: Myelodysplastic Syndromes. Springer: New York. (pp. 89-94).

Haferlach, T., Kern, W. “Classification and Staging of Myelodysplastic Syndromes” in Deeg, H., Bowen, D., Gore, S., Haferlach, T., Beau, M., Niemeyer, C. (eds) (2006) Hematologic Malignancies: Myelodysplastic Syndromes. Springer: New York. (pp.40- 51).

Nimer, S. “Myelodysplastic Syndromes” Blood May 2008. 111: 4841- 4851.

Scott, B., Deeg, J. “Myelodysplastic Syndromes” Annual Review of Medicine 2010. 61:345-358.

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