What are Myelodysplastic Syndromes?

Myelodysplastic syndromes (MDS) are a group of cancers that arise when the bone marrow fails to produce enough normal blood cells to support the body. They are one of the more common diseases of the blood cells in older patients. One in three patients with MDS will go on to develop acute myeloid leukemia, but for many, MDS is a chronic condition that can be controlled with treatment.

MDS occurs when bone marrow cells undergo genetic mutations that affect their ability to make healthy blood cells. Blood cells (including red blood cells, white blood cells, and platelets) develop from stem cells located in the marrow. In cases of MDS, changes in the bone marrow prevent these stem cells (also known as “blasts”) from developing properly: they die quickly or are too malformed (“dysplastic”) to function. As a result, the blood becomes unable to perform essential tasks such as transporting oxygen, fighting infections, and clotting.

How are myelodysplastic syndromes related to leukemia?

Myelodysplastic syndromes used to be known as “pre-leukemia” or “smoldering leukemia” because they can sometimes advance to acute myeloid leukemia (AML). When physicians and scientists recognized that only about a third of patients with myelodysplastic syndromes developed AML, they reclassified MDS as a separate set of conditions.

There are some crucial differences between myelodysplastic syndromes and acute myeloid leukemia. Unlike MDS, AML is diagnosed when more than 20% of the cells in the bone marrow are blast cells. AML typically develops more quickly and severely than MDS and is always a medical emergency. MDS is better regarded as a spectrum of conditions that are less acute, with effects ranging from blood cell shortages and infections to more advanced illness related to increased bone marrow blasts.

Types of MDS

MDS can take on many different forms, depending on the type of blood cells affected, the number of blasts in the bone marrow and bloodstream, and whether or not the chromosomes of the bone marrow cells show abnormalities. The World Health Organization has divided MDS into six categories. Some of the categories are more common than others, and some are more likely to develop into acute myeloid leukemia.

  • MDS with multilineage dysplasia (MDS-MLD): In patients with MDS-MLD, at least 10% of two or more kinds of blood cells (say, red blood cells and white blood cells) are malformed and defective. This means that the patient will also have a shortage of at least one type of blood cell. MDS-MLD is the most common form of myelodysplastic syndromes.
  • MDS with single lineage dysplasia (MDS-SLD): Unlike “multilineage dysplasia,” “single lineage dysplasia” means that only one kind of blood cell shows abnormalities. Patients will have reduced numbers of at least one type of blood cell, but their prognosis is generally better. MDS-SLD is uncommon and unlikely to develop into AML.
  • MDS with ringed sideroblasts (MDS-RS): In MDS-RS, at least 15% of the immature red blood cells are ringed sideroblasts, which means that some of the components of the cell have formed a ring around the cell nucleus. Like MDS with single lineage dysplasia, MDS with ringed sideroblasts is uncommon and probably won’t become AML.
  • MDS with excess blasts (MDS-EB): This type of MDS is characterized by an abnormally high number of blasts (blood stem cells) in the bone marrow and/or bloodstream. Blasts crowd healthy cells. Consequently, patients will also have a shortage of at least one type of blood cell. 25% of cases of MDS fall into this category, and it carries an increased risk of developing into AML.
  • MDS with isolated del(5q): In this type of MDS, the chromosomes of the bone marrow cells lack a portion of chromosome number 5. At least one blood cell type will be abnormal in appearance, and patients will also have low numbers of at least one or two types of blood cells. This is one of the more uncommon forms of myelodysplastic syndromes. It seldom progresses to AML.
  • MDS, unclassifiable (MDS-U): This form of MDS is diagnosed when no other category fits the patient’s condition. It is very uncommon.

When should I see a doctor?

MDS can cause anemia, excessive bruising or bleeding, and more frequent infections. You should see a doctor if you become too exhausted to keep up with your ordinary lifestyle, have abnormally pale skin, observe unusual bleeding or bruising patterns, or find that you are constantly sick. Tell your doctor that you are concerned about MDS.

It’s also important to keep in mind that the symptoms of MDS may not strike you as anything out of the ordinary. Because MDS primarily occurs in elderly populations and its symptoms mimic the normal effects of aging, many people may be unaware that they have it. Some patients only learn that they have MDS after routine bloodwork in their doctor’s office. This is one reason why you should see your doctor regularly for physical exams and recommended testing.