MYELOPROLIFERATIVE DISORDERS IN GENERAL
WHAT IS MYELOPROLIFERATIVE DISEASE (MPD)?
"Myelo" refers to the marrow. Proliferative means growing or reproducing. Disease is an abnormal functioning of an organ or the body. So myeloproliferative disease (MPD) is an abnormal or improper function of or an abnormal growth or reproduction of the marrow.
Our mature circulating blood cells are formed in the marrow. The cells in the marrow responsible for this are called stem cells or "hematopoietic (blood forming) precursor cells. These stem cells have two functions:
- to reproduce themselves to maintain a stem cell pool and
- some of these stem cells need to mature into committed stem cells that will mature into the adult blood cells (RBCs, WBCs, and platelets) that will leave the marrow and enter the circulation.
Myeloproliferative disease is an abnormality of these stem cells so that one of these cell lines (erythroid or RBC, myeloid or WBC, or platelets) undergoes uncontrolled proliferation. This reproduction is no longer under hormonal control. Not all the stem cells need to be abnormal for disease to result. Only one stem cell need escape control for proliferation to occur. This proliferation can then crowd out the normal stem cells. This abnormal clone of stem cells can form all three cell lines but may result in production of one cell line in excess and not produce another cell line in sufficient quantity. This results in overproduction of one or more cell lines and under production of other cell lines. MPD is an improper balance between production (proliferation) of different blood cell lines as much as it is an abnormality of a particular cell line.
TYPES OF MPD
There are 4 types of MPD. These are:
- Chronic Myeloid Leukemia (CML). Affects cells that are developing into white blood cells called granulocytes or neutrophils. Anemia frequently accompanies this condition. Splenomegaly occurs.
- Polycythemia rubra vera (PV). Refers to the true (vera) condition of too many (Poly) red (rubra) cells (cyt) in the blood (hemia) . WBC and platelets are also increased, Itching and splenomegaly are common findings.
- Essential thrombocythemia (ET). Refers to too many platelets in the blood. Other cell types in the blood usually are normal but may be increased.
- Agnogenic myeloid metaplasia (AMM) with myelofibrosis (MF). Agnogenic myeloid metaplasia is an abnormality of red and white blood cells. They do not mature properly. In addition, the marrow has excessive fibrosis (scar tissue formation).
Cause of MPD
Unknown.
Clinical Symptoms
Symptoms and physical finding vary somewhat depending upon which type of MPD is present. There is a great deal of overlap in the clinical features of these various conditions. CML and AMM have anemia. Splenomegaly (enlarged spleen) is found in CML, AMM, and PV. Hepatomegaly (enlarged liver) is found in AMM and CML. Abnormal clot formation in blood vessels occurs in ET and PV and either abnormal clot formation or hemorrhage may result from CML's sluggish blood flow.
MPD patients also have several metabolic abnormalities, which include
- Elevated uric acid levels (seen in 50% of MPD patients) which can result in uric acid kidney stones, uric acid neuropathy, acute gout and chronic gouty arthritis (joint pains).
- Low cholesterol levels especially in those with enlarged spleens
- Elevated histamine levels resulting in pruritus (itching), heartburn, acid eructation (gas), peptic ulcer, small bowel hypermotility, flushing, and angioneurotic edema (swelling of mucous membranes, swelling of skin, etc.). This occurs in 2/3 of MPD patients and reflects the increased basophils in the WBC differential.
- Overall, hypermetabolism producing weakness and fatigue even in the absence of anemia.
DIAGNOSIS
Diagnosis is dependent upon laboratory testing. The basic CBC will give the doctor clues as to which MPD to investigate. Then other tests will be needed to confirm the diagnosis. See individual discussions in depth on the MPD conditions.
STAGING
There is no staging for any of the MPD conditions.
TREATMENT:
Therapy will depend upon type of MPD, the symptoms present, the age, and the overall health of the individual with MPD. See the individual MPD conditions for specific therapy used.
PROGNOSIS
These conditions are slowly progressive. There are no cures (except bone marrow transplantation) but the symptoms can be controlled. In some people the PV, ET, or CML will turn into acute myeloblastic leukemia.
FURTHER INFORMATION SITES/AGENCIES/ETC.
National Cancer Institute: http://www.nci.nih.gov/
MPD home page: http://www.acor.org/diseases/hematology/MPD/
American Cancer Society 1-800-227-2345 www.cancer.org
Leukemia Research Foundation http://www.leukaemia.demon.co.uk/index2.htm
http://oncolink.upenn.edu/pdq/201983.html
http://www.ohsu.edu/cliniweb/handouts/mps.html
http://noah.cuny.edu/cancer/nci/cancernet/101983.html
http://cancer.med.upenn.edu/pdq_html/2/engl/201983.html
