In myeloproliferative neoplasms Overview of Myeloproliferative Neoplasms In myeloproliferative neoplasms (myelo = bone marrow; proliferative = rapid multiplication; and neoplasm = new abnormal growth), the blood-producing cells in the bone marrow (precursor cells... read more . the blood-producing cells Formation of Blood Cells Red blood cells, most white blood cells, and platelets are produced in the bone marrow, the soft fatty tissue inside bone cavities. Two types of white blood cells, T and B cells (lymphocytes)... read more in the bone marrow (precursor cells, also called stem cells) develop and reproduce excessively.
Platelets Platelets The main components of blood include Plasma Red blood cells White blood cells Platelets read more (thrombocytes) are cell-like particles in the blood that help the body form blood clots. Platelets are normally produced in the bone marrow by cells called megakaryocytes. In thrombocythemia, megakaryocytes increase in number and produce too many platelets. Thrombocythemia can be
Primary (essential): Caused by a disorder of platelet-forming cells
Secondary: Caused by a disorder that triggers increased production by normal platelet-forming cells (see secondary thrombocythemia Secondary Thrombocythemia Secondary thrombocythemia is excess platelets in the bloodstream that develops as a result of another disorder and rarely leads to excessive blood clotting or bleeding. Platelets (thrombocytes)... read more )
Essential thrombocythemia usually occurs in people over age 50. Sometimes younger women are affected.
Essential thrombocythemia is considered a myeloproliferative neoplasm, in which certain blood-producing cells Formation of Blood Cells Red blood cells, most white blood cells, and platelets are produced in the bone marrow, the soft fatty tissue inside bone cavities. Two types of white blood cells, T and B cells (lymphocytes)... read more in the bone marrow develop and reproduce excessively. The cause of is a genetic mutation usually in the Janus kinase 2 (JAK2), thrombopoietin receptor (MPL), or calreticulin (CALR) genes. The JAK2 gene mutation causes increased activity of the JAK2 enzyme, a protein that causes excess cell production. The MPL and CALR mutations also increase the activity of JAK2 enzyme, leading to increased blood cell production.
Serious complications are rare but can be life-threatening.
Blood clots may form in almost any blood vessel. Blood clots in large blood vessels may affect the legs (deep vein thrombosis), brain (stroke), heart (heart attack), or lungs (pulmonary embolism). Blood clots in tiny blood vessels can affect the eyes, brain, and skin.
Excessive bleeding also can occur. Although an increased number of platelets might be thought to always cause excessive blood clotting, a very high number of platelets can actually cause bleeding by affecting other parts of the body's clotting system.
Primary thrombocythemia may or may not cause symptoms. When symptoms occur, they are due to the blockage of blood vessels by blood clots and may include
Redness and warmth of the hands and feet, often with burning pain (erythromelalgia)
Tingling and other abnormal sensations in the fingertips, hands, and feet
Loss of vision or seeing spots
Bleeding, usually mild (such as nosebleeds, easy bruising, slight oozing from the gums, or bleeding in the digestive tract)
The spleen may enlarge but this is rare at time of diagnosis and more common in females.
Older people who may already have diseases that cause blood vessel damage, such as diabetes Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more and high blood pressure High Blood Pressure High blood pressure (hypertension) is persistently high pressure in the arteries. Often no cause for high blood pressure can be identified, but sometimes it occurs as a result of an underlying... read more , have a higher risk of complications caused by blood clots, such as transient ischemic attacks Transient Ischemic Attacks (TIAs) A transient ischemic attack (TIA) is a disturbance in brain function that typically lasts less than 1 hour and results from a temporary blockage of the brain’s blood supply. The cause and symptoms... read more , stroke Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction) and symptoms that... read more , and heart attack Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or heart attack (myocardial infarction), depending on the location and amount... read more .
Doctors make a diagnosis of primary thrombocythemia on the basis of the symptoms and after finding increased platelets on a blood count. Other blood tests, including genetic tests for the JAK2, CALR, or MPL mutations are done. In addition, microscopic examination of the blood may reveal abnormally large platelets, clumps of platelets, and fragments of megakaryocytes.
To distinguish primary thrombocythemia from secondary thrombocythemia Secondary Thrombocythemia Secondary thrombocythemia is excess platelets in the bloodstream that develops as a result of another disorder and rarely leads to excessive blood clotting or bleeding. Platelets (thrombocytes)... read more , which has many known causes, doctors look for signs of other conditions that could increase the platelet count. Removal of a sample of bone marrow for examination under a microscope (bone marrow biopsy Bone Marrow Examination Red blood cells, most white blood cells, and platelets are produced in the bone marrow, the soft fatty tissue inside bone cavities. Sometimes a sample of bone marrow must be examined to determine... read more ) and doing genetic testing on the cells are sometimes helpful.
Aspirin, which makes platelets less sticky and impairs clotting, may be given in small doses to help relieve mild symptoms such as redness and warmth of hands and feet, and headache, but people with significant bleeding should not take aspirin.
Thrombocythemia may also require treatment with a drug that decreases platelet production. Such drugs include hydroxyurea, anagrelide, interferon-alpha, and ruxolitinib.
Treatment with one of these drugs is typically started when clotting or bleeding complications develop and not just based on the platelet count.
If drug treatment does not slow platelet production quickly enough, it may be combined with or replaced by plateletpheresis Plateletpheresis (platelet donation) In addition to normal blood donation and transfusion, special procedures are sometimes used. In plateletpheresis, a donor gives only platelets rather than whole blood. Whole blood is drawn from... read more , a procedure reserved for emergency situations. In this procedure, blood is withdrawn, platelets are removed from it, and the platelet-depleted blood is returned to the person. However, plateletpheresis is inefficient and only a temporary solution.
People with essential thrombocytosis usually have a normal life span, but some develop polycythemia vera Polycythemia Vera Polycythemia vera is a myeloproliferative neoplasm of the blood-producing cells of the bone marrow that results in overproduction of all types of blood cells. Polycythemia vera is due to mutations... read more (usually women) or myelofibrosis Myelofibrosis Myelofibrosis is a disorder in which fibrous tissue in the bone marrow replaces the blood-producing cells, resulting in abnormally shaped red blood cells, anemia, and an enlarged spleen. Myelofibrosis... read more (usually men).
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
MPN Research Foundation: supports research as well as advocacy and education for people with myeloproliferative neoplasms