Definition & Overview
Myeloproliferative disorders refer to a number of diseases that are caused by the bone marrow's excessive production of white and red blood cells and platelets. The bone marrow normally produces immature blood stem cells that develop into mature blood cells through a gradual step-by-step process. First, the stem cell develops into either a lymphoid or myeloid stem cell. A lymphoid stem cell then develops into a white blood cell, while a myeloid stem cell can develop into any one of the three types of mature blood cell: red blood cells, white blood cells, or platelets.
The role of red blood cells is to carry oxygen and nutrients to the tissues all over the body, while white blood cells ward off infections and diseases. Platelets, on the other hand, stop bleeding and the formation of blood clots. In myeloproliferative disorders, there is an excess amount of blood stem cells that become one or more types of mature cells. These are progressive disorders that get worse as more and more blood cells are produced.
Cause of Condition
Myeloproliferative disorders are caused by the excess production of white blood cells, red blood cells, or platelets. They come in six different diseases, depending on which type of blood cell is being excessively produced.
Chronic myelogenous leukemia – This is a characterized by excess amounts of white blood cells in the bone marrow.
Polycythemia vera – This is characterized by the thickening of the blood due to excessive red blood cells, but there is also a tendency for white blood cells and platelets to increase. This disease may cause the extra blood cells to accumulate in the spleen and cause swelling. Due to the increased number of red blood cells, and possibly of platelets, the patients, particularly those who are 65 years and older, face an increased risk of stroke and heart attack.
Primary myelofibrosis (or chronic idiopathic myelofibrosis) – This is a disease wherein all three types of blood cells build up in abnormal amounts inside the bone marrow. These blood cells do not mature properly and cause the thickening of the fibers inside the bone marrow. They then slow down the marrow’s ability to form new blood cells, until it begins making fewer and fewer blood cells; a task that is then taken upon by the liver and spleen.
Essential thrombocythemia – This disease is caused by an excess amount of platelets in the bone marrow and blood.
Chronic neutrophilic leukemia – This occurs when a large number of blood stem cells develop into neutrophils, a form of white blood cell known for its role in fighting infection. Neutrophils work by surrounding then destroying dead cells and foreign substances, such as bacteria and viruses. However, it causes several negative effects when there is too much of it in the body.
Chronic eosinophilic leukemia – This occurs when too many eosinophils are produced in the bone marrow. Eosinophils are another type of white blood cell and their role is to react to allergens and cause allergic responses in the body. The excess amount of eosinophils may spread to the blood and other tissues.
The symptoms of myeloproliferative disorders tend to differ based on the specific type that the patient is suffering from.
Chronic myelogenous leukemia – This causes fatigue, anorexia or unexplained weight loss, abdominal discomfort, swollen and painful joints that may develop into gouty arthritis or hyperuricemia, and easily bruising or bleeding.
Polycythemia vera –This disease may cause the extra blood cells to accumulate in the spleen and cause swelling. Patients may also experience some pressure or fullness below the left rib, double vision, headaches, weakness, itching (usually all over the body after exposure to warm or hot water), dizziness, unexplained weight loss, and reddening of the face like sunburn.
Primary myelofibrosis – Patients may experience pain below the left rib and a general feeling of tiredness. They may also experience shortness of breath, feeling full faster when eating, easily bleeding or bruising, fever, night sweats, and weight loss. They may also develop petechiae, which are flat, red spots that form under the skin and are caused by bleeding.
Essential thrombocythemia – This disease is hard to diagnose because it usually does not present any noticeable symptoms, especially in its early stages. The only symptoms that may be experienced include headaches, redness, burning or tingling sensation in the hands or feet and vision and hearing problems. The platelets also become sticky, which may lead to the formation of abnormal blood clots that increases the risk of stroke and heart attack.
Chronic neutrophilic leukemia – Patients who have neutrophilic leukemia may suffer from spleen and liver inflammation due to the excess amount of neutrophils.
Chronic eosinophilic leukemia – The main symptoms of eosinophilic leukemia are a feeling of tiredness as well as fever, cough, muscle pain, itching, and diarrhea. Some swelling under the skin may also be observed on the hands and feet, eyes, lips, and throat.
In chronic cases of myeloproliferative disorders, especially those involving an excess production of white blood cells, there is a risk for the disorder to develop into acute leukemia.
Who to See & Types of Treatments Available
Patients who are suspected of suffering from chronic myeloproliferative disorders are advised to consult their family doctor or a general physician. To confirm the presence of the disorder, certain tests such as a physical exam, a review of the patient’s medical history, a complete blood count or CBC, a peripheral blood smear, and blood chemistry tests will be performed. The patient will also undergo a bone marrow biopsy or aspiration, wherein a small piece of the bone as well as bone marrow blood samples are taken from the body using a hollow needle called the Jamshidi. This procedure is performed either on the hip or breast bone and is intended to allow doctors to examine the tissue and look for abnormal cells. This procedure is known to cause some pain.
Other advanced procedures may also be required after a biopsy has been conducted; these include cytogenetic analysis, a test wherein the tissue samples taken are studied under a microscope to look for chromosomal changes, which can help rule out certain disorders. Another procedure is the JAK2genemutation test, a lab test that checks for the specific JAK2 gene mutation, which is present in patients with certain types of myeloproliferative disorder, specifically polycythemia vera, idiopathic myelofibrosis, or essential thrombocythemia.
Once diagnosed, the treatment that patients will undergo will depend on certain factors:
- The type of myeloproliferative disorder
- Number of abnormal blood cells
- Number of blasts, or blood cells that do not mature normally
- Chromosomal changes, if any
- Symptoms experienced by the patient
There are 11 types of standard treatment options for myeloproliferative disorders:
- Watchful waiting
- Platelet apheresis
- Transfusion therapy
- Radiation therapy
- Drug therapy using prednisone, danazol, anagrelide, thalidomide, lenalidomide, or pomalidomide
- Surgery, namely splenectomy (when the spleen has become enlarged)
- Biologic therapy
- Targeted therapy
Stem cell transplant with high-dose chemotherapy
National Cancer Institute (NCI)