What are myelodysplastic syndromes (MDS)?

Myelodysplastic syndromes are also called myelodysplasia or MDS for short. This group of conditions causes a drop in the number of normal blood cells. 

Myelodysplastic syndromes get their name from myelo, meaning bone marrow, and dysplasia, meaning abnormal growth.

The bone marrow is the soft inner part of our bones that makes blood cells. All blood cells start from the same type of cell called a stem cell. The stem cell makes immature blood cells. The immature cells go through various stages of development before they are released into the blood as fully developed blood cells.

These include:

  • red blood cells to carry oxygen around our bodies
  • white blood cells to fight infection
  • platelets to help the blood clot
A simplified diagram showing how blood cells are made

With myelodysplastic syndromes, the bone marrow doesn't make enough normal blood cells. The blood cells it does make are not fully developed and not able to work normally.

These abnormal blood cells then either stay in the bone marrow or are destroyed before they get into the bloodstream. As the condition develops, the bone marrow becomes full. The immature blood cells then spill out into the bloodstream.

The low numbers of normal blood cells in the bloodstream eventually cause symptoms. The symptoms may be difficult to control.

Myelodysplastic syndromes can occur in people of any age but are most common in people over 70 years old.

Causes of MDS

We don't know what causes most cases of MDS. This is called primary MDS.

More rarely MDS is caused by radiotherapy or chemotherapy treatment for cancer. This is called secondary or treatment related MDS.

We do know of some risk factors that makes the risk of developing MDS more likely. One of these is exposure to the chemical benzene. People are most likely to come into contact with benzene through their work. It is used in the rubber industry and is one of the chemicals in petrol. It is also in cigarette smoke.

Signs and symptoms of MDS

Some people with a myelodysplastic syndrome do not have any symptoms at all. Their MDS is picked up on a routine blood test for something else.

For most people, symptoms tend to be mild at first and get worse slowly. The symptoms are caused by a drop in the number of blood cells and could include:

  • tiredness and sometimes breathlessness because of a low red blood cell count (anaemia)
  • frequent infections because of a low white blood cell count
  • bleeding (such as nosebleeds) or bruising easily because of a low platelet count

You might have pain or discomfort in your tummy (abdomen) from an enlarged spleen.

Types of MDS

There are different types of myelodysplastic syndrome (MDS). Some affect one type of blood cell, others affect all types of blood cells.

MDS can develop slowly or quickly depending on the type you have.

Doctors divide the different types of MDS into groups or subtypes. The system they use is called a classification system. The most commonly used classification system for MDS in the UK is the World Health Organisation (WHO) system. It was last updated in 2016. Specialists are learning more about MDS all the time.

The WHO system generally looks at:

  • how many immature cells (blasts) there are in the blood
  • how many immature cells (blasts) in bone marrow
  • how normal the blood cells are

The system is quite complicated, and your doctor or nurse can explain it in more detail.

Different types of MDS

You can read about the main types of MDS below.

MDS with single lineage dysplasia (MDS-SLD)

This affects a single type of blood cell. You might have low numbers of:

  • red blood cells (anaemia)
  • white blood cells (neutropenia)
  • platelets (thrombocytopenia)

Before 2016, doctors used to describe MDS-SLD as refractory cytopenia with unilineage dysplasia (RCUD).

MDS with ring sideroblasts (MDS-RS)

There are low numbers of red blood cells (anaemia). And a number of early red blood cells in the bone marrow have a ring of iron in them. These cells are called ring sideroblasts.

There are two subtypes of MDS-RS:

  • MDS-RS-SLD – This means MDS with single lineage dysplasia and ring sideroblasts. Single lineage dysplasia means the MDS affects a single type of blood cell.
  • MDS-RS-MLD – This means MDS with multiple lineage dysplasia and ring sideroblasts. Multiple lineage dysplasia means the MDS affects more than one type of blood cell.

MDS with multilineage dysplasia (MDS-MLD)

The MDS affects more than one type of blood cell. So, two or more of your blood cell levels will be low. There are very few or no immature cells (blasts) in the blood. There are a small number of blasts in the bone marrow.

Before 2016, doctors used to call this refractory cytopenia with multilineage dysplasia (RCMD).

MDS with excess blasts (MDS-EB)

One or more of your blood cell levels are low, and many of these cells look abnormal in the bone marrow. There are a greater number of immature cells (blasts) in the blood and bone marrow than in other types of MDS. There are two subtypes of MDS-EB.

MDS-EB is split into MDS-EB-1 and MDS-EB-2. In MDS-EB-2, there are more blast cells in the blood and bone marrow than in MDS-EB-1.

Before 2016 doctors used to call this disorder refractory anaemia with excess blasts.

Myelodysplastic syndrome associated with isolated del (5q) or with one extra chromosome change

With this type, the cells in the bone marrow have a chromosome change called isolated del (5q). There are low numbers of red cells in the blood (anaemia). The platelet count is usually normal or high.

Myelodysplastic syndrome unclassified (MDS-U)

This covers any type of MDS that does not fit into one of the above groups.

Risk groups for MDS

As well as the different types of MDS, doctors group MDS according to how the disease is most likely to develop.

In some, but not all, MDS will develop into a of type blood cancer called acute myeloid leukaemia (AML). Doctors call this transformation. Some types of MDS have a higher risk of transforming into AML than others.

Transformation might happen after a few months for some types of MDS but after several years for others. You can ask your doctor about the risk of transformation with your type of MDS.

Revised International Prognostic Scoring System (IPSS-R)

The system for grouping MDS according to likely outcome is called the Revised International Prognostic Scoring System (IPSS-R). There are 5 risk groups:

  • very low risk
  • low risk
  • intermediate risk
  • high risk
  • very high risk

The risk group depends on:

  • the number of immature cells (blasts) in your bone marrow and blood
  • your blood cell levels
  • whether there are chromosome Open a glossary itemchanges in the affected blood cells

Knowing what type of MDS you have, and your risk score helps your doctor to decide on the best treatment for you.

Last reviewed: 
20 Jul 2020
Next review due: 
20 Jul 2023
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