Types of Myeloproliferative Disorders

NYU Langone hematologists, doctors who specialize in blood conditions, diagnose and manage all types of myeloproliferative disorders. These are a group of conditions in which the bone marrow produces too many blood cells.

Blood cells develop from stem cells. These immature cells, produced in the bone marrow, divide and mature into different types of blood cells. These include white blood cells, which help fight infection; red blood cells, which carry oxygen and other nutrients to the body’s tissues and organs; and platelets, which help with blood clotting.

During cell division, mistakes in copying the genetic material lead to gene mutations in blood-forming stem cells. The mutation typically occurs spontaneously, rather than being inherited from a parent. Different mutations are responsible for the growth of one or more types of blood cells, resulting in a particular myeloproliferative disorder.

Hematologists at Perlmutter Cancer Center can recommend tests to detect these genetic mutations that help determine if the cause of high blood cell levels is a myeloproliferative disorder.

These disorders are usually chronic, meaning lifelong. They are often slow growing and can be managed with ongoing care. Rarely, myeloproliferative disorders can become more aggressive and progress to a fast-growing form of blood cancer called acute myeloid leukemia (AML).

There are several types of myeloproliferative disorders. The most common are polycythemia vera, essential thrombocythemia, primary myelofibrosis, and chronic myelogenous leukemia (CML).

Polycythemia Vera

Most people with polycythemia vera have a mutation in a gene called Janus kinase 2 (JAK2). This mutation increases the number of red blood cells produced. As red blood cells multiply and mature, they leave the bone marrow and enter the bloodstream. This leads to a rise in the number of red cells and the level of hemoglobin, the protein in red blood cells that carries oxygen, both of which eventually cause the blood to thicken. The thickened blood flows more slowly than usual, preventing enough oxygen from reaching organs and other tissues. It also can cause the blood to clot.

Levels of other blood cells, including white blood cells and platelets, can also become too high. High levels of platelets can further contribute to blood clotting.

Symptoms of polycythemia vera include red and itchy skin—especially after a hot bath or shower—fatigue, fevers, weight loss, and night sweats.

Because the condition contributes to blood clotting, complications may include deep vein thrombosis, which is a blood clot in a vein, and pulmonary embolism, which is a blood clot that travels to the lungs, as well as heart attack and stroke.

If polycythemia vera progresses, blood cell production can expand to the spleen, which is an organ in the abdomen that normally filters the blood. As the spleen produces more blood cells, it enlarges and may become painful, a condition called splenomegaly. Advanced polycythemia vera can cause scar tissue to form in the bone marrow, a condition called secondary myelofibrosis.

Although there are no known risk factors associated with polycythemia vera, it is more common in people older than age 60.

Essential Thrombocythemia

In essential thrombocythemia, another myeloproliferative disorder, the bone marrow produces too many cells called megakaryocytes, which eventually develop into platelets. Platelets are the blood-clotting cells, and abnormalities in their number and function can increase the risk of clotting and bleeding.

Symptoms of essential thrombocythemia include fatigue, fevers, weight loss, and night sweats.

Complications of clotting, such as deep vein thrombosis, pulmonary embolism, heart attack, or stroke, can also happen. Sometimes, high platelet levels can lead to bruising or bleeding. The condition can also cause an enlarged spleen because of abnormal blood cell production there, leading to signs and symptoms of splenomegaly.

Rarely, essential thrombocythemia can progress to a condition called secondary myelofibrosis, in which scar tissue forms in the bone marrow. This leads to decreased blood production in the marrow and an enlargement of the spleen, as it tries to compensate by making blood cells.

The cause of essential thrombocythemia is often gene mutations in the Janus kinase 2 (JAK2), the calreticulin (CALR), or the MPL proto-oncogene. The result of these genetic mutations is uncontrolled megakaryocyte production, leading to increased platelet levels.

Essential thrombocythemia is more common in women than in men and in people older than age 60.

Primary Myelofibrosis

In primary myelofibrosis, stem cells divide uncontrollably, creating many new abnormal cells. The increased number of cells, along with the proteins they may secrete, can cause scar tissue to form in the bone marrow, which interferes with healthy blood cell production.

As a result, immature or malformed red blood cells develop. This causes a decrease in levels of healthy red blood cells in the body, leading to anemia, which causes weakness and fatigue.

Abnormal stem cells can also increase or decrease platelet production. Lower levels of healthy platelets can lead to bruising or bleeding, and higher levels can cause the blood to clot.

Myelofibrosis can also contribute to higher or lower levels of healthy white blood cells. Lower levels can cause increased infections; higher levels can cause the blood to become more viscous, meaning sticky and thick, which can lead to stroke or abnormal bleeding.

As myelofibrosis progresses, scar tissue can form in the bone marrow, causing bone pain. As abnormal blood cells circulate in the bloodstream and collect and grow in the spleen, it enlarges. This can cause abdominal pain and swelling.

Primary myelofibrosis is linked to mutations in the genes Janus kinase 2 (JAK2), calreticulin (CALR), and MPL proto-oncogene. The condition is most often found in people older than age 50. Myelofibrosis may also develop in people who have polycythemia vera or essential thrombosis. When it does, it is called secondary myelofibrosis.

Either primary or secondary myelofibrosis can increase a person’s risk of developing AML, a fast-growing cancer in which immature red and white blood cells and platelets fail to mature into healthy cells.

Chronic Myelogenous Leukemia

Chronic myelogenous leukemia, commonly known as CML, is a condition in which the bone marrow produces too many mature and immature white blood cells.

CML is caused by a genetic mutation that occurs in the chromosomes of the blood cells, when genes on two specific chromosomes move from one to another, changing the length of each. This creates a gene mutation, or fusion gene, called BCR-ABL, also known as the Philadelphia chromosome. This new gene results in the production of an enzyme called tyrosine kinase, which promotes the activity and growth of immature white blood cells called myeloid cells in the bone marrow.

CML progresses slowly, with white blood cells accumulating in the bone marrow, blood, and spleen over years.