Leukemia & Lymphoma Society - Myeloproliferative Disorders

Myeloproliferative disorders are a group of blood diseases characterized by chronic increases in some or all of the blood cells. This group of blood disorders includes

Polycythemia vera
Essential (or primary) thrombocythemia
Idiopathic myelofibrosis

All blood cells start out as hemopoietic (blood-forming) stem cells with the potential to become red cells, white cells, or platelets. Myeloproliferative disorders begin with a change to the DNA of a single stem cell in the marrow, where blood cells are made.

Polycythemia vera is a disease in which the red cells are the main cells that are increased beyond normal levels. In many patients, white blood cell and platelets counts are also elevated.

Complications result mainly from the increase in red cells and in platelets: too many red blood cells make it difficult for the blood to flow smoothly; too many platelets can lead to the formation of blood clots; and underlying vascular disease, commonly found in older people, can increase the risk of serious complications, such as strokes or heart attacks.

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Essential (or primary) thrombocythemia is a disease in which the platelets are the main cells that are increased beyond normal levels.

The normal formation of platelets consists of stem cells forming a few very large cells in the marrow called megakaryocytes. Each of the megakaryocytes generates hundreds or thousands of platelets. In essential thrombocythemia, the altered stem cells produce an excessive number of megakaryocytes. The end result is abnormally high levels of platelets in the blood. When present in very large numbers, these platelets may not function normally and can cause blockages in blood vessels or bleeding problems.

Click here to read more about essential (or primary) thrombocythemia.

Idiopathic myelofibrosis is a disease in which scar-like tissue forms in the marrow as a result of abnormal production of red cells, white cells, and platelets.

Too few red cells are made, and usually too many white cells and megakaryocytes. The excessive production of megakaryocytes leads to abnormally high levels of platelets in the blood. The overproduction of abnormal megakaryocytes also releases chemicals in the marrow that lead to the production of fibrous (scar-like) tissue in the marrow.

Click here to read more about idiopathic myelofibrosis.