What Are The Different Types Of Myelodysplastic Syndrome?

Myelodysplastic syndrome (MDS) is a type of cancer in the bone marrow which is the primary site of hematopoiesis. Bone marrow produces stem cells which differentiate into matured red blood cell (RBC), white blood cells (WBC) and platelets. In myelodysplastic syndrome these stem cells develop into abnormal cells called dysplastic cells and blast cells which are immature stem cells. So, there are not any mature healthy blood cells in the blood which leads to symptoms such as anemia, recurrent infections, and bleeding disorders; most myelodysplastic syndrome progress into acute myeloid leukemia (AML).

There are many classification systems, World Health Organization (WHO) classifications are the used widely, and it classifies myelodysplastic syndrome according to their appearance microscopically along with some other features.

The features are:

• How many early types of RBC, WBC, and platelets show dysplasia?
• The severity of cytopenia (reduction of all blood cell types) of the person
• The portion of early RBC which are ring sideroblasts (around the nucleus a ring of iron deposition)
• The amount of blasts cells in the bone marrow.
• Any chromosomal changes in the bone marrow⁽¹⁾
• Based on these there are 6 types of myelodysplastic syndrome
• Myelodysplastic Syndrome With Multilineage Dysplasia (MDS-MLD)
• This is the commonest type
• Dysplasia is seen in at least 10% of blood cells and at least in 2 cell types.
• At least one cell type is low
• Less than 5% of blast cells (normal) in the bone marrow. Blast cells are not present in the blood.
• Myelodysplastic Syndrome With Single Lineage Dysplasia (MDS-SLD)
• This is an uncommon type and if present patient progress into acute
• Dysplasia is seen in at least 10% of blood cells and at least in 1 cell type.
• One or two cell type are low but other cell type/s are normal
• Less than 5% of blast cells (normal) in the bone marrow. Blast cells are not present in the blood.
• Less common type and rarely progress into AML. Most patients live long without treatment.

This type the patients have more blasts cells in the bone marrow and/or blood, more dysplasia in cells and at least one cell type is very low in numbers.

• Divided into two groups according to the number of blasts in the bone marrow and blood
• MDS-EB1 – 5-9% of cells are blast cells in the bone marrow or 2-4% of cells are blast cells in the blood
• MDS-EB2 – 10-19% of cells are blast cells in the bone marrow or 5-19% of cells are blast cells in the blood
• Seen in 1 in 4 cases and most likely to progress into AML, MDS-EB2 has the highest risk.

Many of the early RBC are ring sideroblasts and the diagnosis is made when 15% of early RBC are ring sideroblasts or if 5% of cells have an abnormality in the SF3B1 gene. Divided into two based on the number of cell types show dysplasia

• MDS-RS with single lineage dysplasia (MDS-RS-SLD): dysplasia seen in only one cell type
• MDS-RS with multilineage dysplasia (MDS-RS-MLD): dysplasia is seen in more than one cell type
• Rare type of myelodysplastic syndrome and rarely progress into AML, these patients have a good prognosis.
• Myelodysplastic Syndrome With Isolated del(5q)
• Dysplasia is seen in at least in 1 cell type.
• One or two cell type are low usually RBC
• Abnormality in chromosome 5

Rare type of myelodysplastic syndrome seen commonly in elderly women; for an unknown reason, these patients have a good prognosis and rarely progress into AML

It is a rare type and features do not fit any other types of myelodysplastic syndrome.⁽¹⁾

There are many classification methods of myelodysplastic syndrome, WHO classification is commonly used where it classifies MDS according to their appearance microscopically along with some other features. There are 6 types myelodysplastic syndrome with multilineage dysplasia (MDS-MLD) which is the commonest type, myelodysplastic syndrome with single lineage dysplasia (MDS-SLD), MDS with excess blasts (MDS-EB) most likely to progress into AML, MDS with ring sideroblasts (MDS-RS), MDS with isolated del(5q), and myelodysplastic syndrome, unclassifiable (MDS-U)

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