There are four main types of myeloproliferative disorders (MPD):
- Chronic myelogenous leukemia (CML) is associated with an overproduction of specialized white blood cells, called granulocytes.
- Polycythemia mera (PV) occurs when too many red blood cells are made.
- Myelofibrosis (MF) with agnogenic myeloid metaplasia is associated with increased fibrosis in the bone marrow, resulting in a markedly enlarged spleen and low red blood cells (anemia).
- Essential thrombocythemia (ET) occurs when there are too many platelets in the blood.
Patients with MPD can have many or few symptoms depending on how abnormal their blood counts become. Those with ET and PV have "thick" blood that is more prone to clotting and is associated with heart attacks, strokes and clots in leg veins. Patients with chronic myelogenous leukemia (CML) and myelofibrosis (MF) often feel tired and report pain or fullness in their belly from an enlarged spleen.
Signs and symptoms of MPD include:
- Moderate or severe anemia, a condition where there are not enough red blood cells to carry oxygen
- Pale skin
- Weakness and fatigue
- Shortness of breath during exertion
- Loss of appetite
- Prolonged bleeding from minor cuts due to low platelet counts
- Purpura, a condition in which the skin bleeds. This causes black and blue or pin-sized spots on the skin
- Sinus, skin or urinary infections due to low white blood cell counts
Though myeloproliferative disorders are serious, and may pose certain health risks, people with these conditions often live for many years after diagnosis. The prognosis largely depends on the type of disorder.
All myeloproliferative disorders are caused by overproduction of one or more types of cells. No one knows what triggers the overproduction of cells, but theories include:
- Genetics -- Some people with CML have an abnormally shortened chromosome known as the Philadelphia chromosome.
- Environment -- Some studies suggest that myeloproliferative disorders may result from an overexposure to radiation, electrical wiring, or chemicals.
There is no cure for most myeloproliferative disorders. However, there are several treatments that help improve symptoms and prevent complications associated with the conditions.
The treatment for each type of myeloproliferative disorder is slightly different:
- PV -- lower red blood cell count by removing blood (phlebotomy). Treatment with medication, called myelosuppressive therapy, is also available.
- ET -- treat symptoms, when present, with medications
- MF -- treat symptoms, when present, with medications
- CML -- bone marrow transplant is the only potential cure. Some medications (such as interferon) are used experimentally.