Myelodysplastic Syndromes

 

Myelodysplastic syndrome is an umbrella term for a group of bone marrow disorders, where the blood cells (immature) in the bone marrow do not mature properly or develop as healthy blood cells. It is estimated that the annual incidence for myelodysplastic syndromes is about 4.9 cases for every 100,000 people.

Brief overview

The bone marrow is a soft spongy tissue found in most of the bones. It produces immature cells known as stem cells that can differentiate into three kinds of blood cells- red blood cells, white blood cells and platelets. The fully developed, mature, and functional blood cells leave bone marrow to enter the bloodstream. In myelodysplastic syndrome, the stem cells in the bone marrow may not mature or they may turn out as damaged or defective blood cells. Hence, individuals with myelodysplastic syndrome have immature or fewer circulating blood cells in their body.

Based on the number of blood cells affected and many other factors, myelodysplastic syndromes are categorized into several types. However, in about one in three patients, myelodysplastic syndrome may progress to become an aggressive cancer of the bone marrow cells known as acute myeloid leukemia (AML).

Types of myelodysplastic syndromes

Depending on the type of blood cells involved, myelodysplastic syndromes are divided into following subtypes.

Myelodysplastic syndrome with unilineage dysplasia - One blood cell type is low in number and appears abnormal under the microscope

Myelodysplastic syndrome with multilineage dysplasia - Two or three blood cell types are abnormal, with low numbers of at least 2 types of blood cell types.

Myelodysplastic syndrome with ringed sideroblasts - Red blood cells in the bone marrow contain a ring of excess iron around the nucleus known as ring sideroblasts. The white blood cell and platelet counts are usually normal.

Myelodysplastic syndrome associated with isolated del chromosome abnormality - Low numbers of red blood cells with specific mutation (deletion of 5q chromosome) in their DNA.

Myelodysplastic syndrome with excess blasts - Any of the three types of blood cells may be low and appear abnormal under a microscope. Very immature blood cells are observed in the blood and bone marrow.

Myelodysplastic syndrome, unclassified - Reduced numbers of one of the three types of mature blood cells, with no specific signs of the other MDS subtypes. Either the white blood cells or platelets may look abnormal under a microscope.

 

Causes and risk factors of myelodysplastic syndromes

In most cases, the cause of the myelodysplastic syndromes remains unknown. However certain factors can increase the chance of developing myelodysplastic syndromes. They include:

  • Receiving cancer treatments, such as chemotherapy and radiation therapy
  • Exposure to toxic chemicals, such as tobacco, benzene, and pesticides
  • Exposure to heavy metals, such as lead or mercury

Typically, myelodysplastic syndromes are more common for people aged around 75 years. Also, men are more likely to develop this condition compared to women.

Signs and symptoms of myelodysplastic syndromes

Typically, patients with myelodysplastic syndrome at its earlier stage, may not experience any symptoms. However, there are two common features found in myelodysplastic syndrome patients. Firstly, they have low blood cell count for at least one type of blood cell. Secondly, the blood cells in their bone marrow and blood look abnormal in shape or size.

The symptoms if they do occur may include:

  • Shortness of breath
  • Fatigue
  • Unusual paleness because of anemia (low red blood cell count)
  • Easy bruising or bleeding due to thrombocytopenia (low blood platelet count)
  • Pinpoint-sized red spots under the skin caused by bleeding (petechiae)
  • Frequent infections attributable to leukopenia (low white blood cell count) 

Diagnosis

Diagnosis for myelodysplastic syndromes could be difficult as the symptoms are not specific for the condition and are common to many other conditions. Also, there are no specific tests that indicate the presence of the condition. Hence, several types of tests are performed to rule out other conditions and create a treatment plan.  

Medical History

A detailed medical history may be obtained along with information related to past exposure to harmful chemicals or cancer treatments such as radiation therapy or chemotherapy. 

Blood Tests

Several types of blood tests are used to determine the number of blood cells and to find out any abnormalities related to their shape, size, and appearance.

Complete Blood Count (CBC): CBC is a basic test that is used to check whether the numbers of various blood cell types fall within the reference ranges. Any abnormalities in this test could be implied as the first sign of the condition. Following any suspicious results, a blood smear test may eb advised, which involves examining the cells under the microscope for the presence of dysplasia (abnormal growth of the cells).

Blood tests that measure other components such as iron, erythropoietin, vitamin B12 and folates help to rule out other conditions and determine the exact cause for the disease.

Bone Marrow Tests

A bone marrow test is the mainstay for diagnosis of myelodysplastic syndromes. During the procedure, the liquid bone marrow is obtained from the pelvic or breastbone using a hollow needle, in a process known as bone marrow aspiration. Subsequently, a solid piece of the bone marrow is also removed, in a process known as bone marrow biopsy. The samples obtained are tested in many ways to diagnose the condition, monitor the response to treatment and provide information about the prognosis of the condition. Listed are the tests performed on the bone marrow samples.

  • Histochemistry studies: During the histological analysis, the cells are examined under the microscope to look for any abnormalities related to myelodysplastic syndromes. They also help to determine the bone marrow blast (immature blood cell) count and to find other causes for bone marrow malfunction.
  • Cytogenetic studies: These studies help determine changes in the structure of the chromosome in the bone marrow cells sampled. About 50% of people with myelodysplastic syndromes have one or more chromosomal changes, most of them seen in the chromosomes 5, 7, 8, and 20.
  • Flow cytometry: During flow cytometry, the sampled cells are passed through a laser beam that enables to effectively look for dysplasia and estimate the blast count.
  • Molecular testing: Molecular studies are more precise that look for DNA mutations in the cells. These tests determine the specific genetic characteristics of bone marrow cells.

Myelodysplastic syndromes staging

According to the French American British (FAB) system, the different stages of myelodysplastic syndromes include:

  • Refractory anemia - Blasts less than 5%
  • Refractory anemia with ring sideroblasts – Blasts less than 5%
  • Refractory anemia with excess blasts in transmission (Acute myelogenous leukemia) - Blasts 5-20%
  • Refractory anemia with excess blasts in transformation - Blasts 21-30%
  • Chronic myelomonocytic leukemia - Blasts 5-20%

Treatment

The treatment for myelodysplastic syndrome predominantly involves managing the symptoms and slowing the disease progression. People with no symptoms are monitored regularly to see if the disease progresses.

Blood transfusions

Blood transfusions may be used to replace red blood cells, white blood cells or platelets. They help to treat symptoms like anemia, fatigue, and shortness of breath in patients with myelodysplastic syndromes.

Medications

The common medications used in the treatment of myelodysplastic syndromes include:

Growth factors – These helps promote blood cell production and reduce the need for blood transfusions.

Chemotherapy – This therapy helps kill the abnormal cells of the bone marrow and bring back its ability to produce functional blood cells. It also helps to reduce the risk of acute myeloid leukemia.

Immune modulators – These agents suppress the myelodysplastic syndrome cells and also alter the immune system. It works well for mild myelodysplastic syndrome and in people with deletion of 5q chromosome.

Immune suppressants – These drugs are used to suppress the immune system and reduce the need for red blood transfusions.

Antibiotics - Infections are frequent complications in patients with myelodysplastic syndrome either due to low blood counts or immune therapies. Hence, antibiotics may be recommended to treat infections.

Bone marrow transplant

A bone marrow transplant (stem cell transplant) is often a curative treatment for myelodysplastic syndromes, where the patient receives new stem cells that can grow into healthy blood cells in the bone marrow. During the procedure, high doses of chemotherapy is used to kill the defective blood cells in the bone marrow and then are replaced with healthy cells obtained from a donor (allogeneic transplant).

Prognosis

The prognosis is determined based on the results obtained from diagnostic tests. The blood counts, percentage of immature blood cells (blast cells) in the bone marrow, and the types of chromosomal abnormalities together affect the prognosis of the condition. The average survival for a patient with mild disease at the time of diagnosis could be around 5.7 years, and 0.4 years for a patient with severe disease.

References:
  1. Myelodysplastic syndromes https://www.mayoclinic.org/diseases-conditions/myelodysplastic-syndrome/diagnosis-treatment/drc-20366980 Accessed on 28.August.2020
  2. Myelodysplastic Syndrome (MDS) https://www.mskcc.org/cancer-care/types/myelodysplastic-syndrome Accessed on 28.August.2020
  3. Myelodysplastic Syndromes https://www.ucsfhealth.org/conditions/myelodysplastic-syndromes Accessed on 28.August.2020
  4. All About Myelodysplastic Syndromes (MDS) https://www.oncolink.org/cancers/leukemia/myelodysplastic-syndromes-mds/all-about-myelodysplastic-syndromes-mds Accessed on 28.August.2020
  5. Myelodysplastic Syndrome (MDS) https://media.leukaemiacare.org.uk/wp-content/uploads/Myelodysplastic-Syndromes-MDS-Web-Version.pdf Accessed on 28.August.2020
  6. MDS - Myelodysplastic Syndromes https://www.aamds.org/diseases/mds Accessed on 28.August.2020
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