polycythemia vera
Meaning of polycythemia vera: The word vera, Latin for true, separates it from a rise in red cells that is merely a reaction to something else.
Definition of polycythemia vera
Polycythemia vera is a chronic blood cancer in which the bone marrow produces far too many red blood cells. White cells and platelets are frequently raised as well, but the excess of red cells defines it. The extra cells thicken the blood and slow its passage through small vessels, which is why the main hazard is clotting rather than bleeding.
What drives the overproduction?
Red cell production is normally commanded by erythropoietin, a hormone released by the kidney when oxygen levels fall. That signal is relayed inside the cell by a protein called JAK2. In nearly everyone with this condition, an acquired change in the JAK2 gene leaves the relay switched on permanently, so the bone marrow behaves as though the hormone were constantly arriving even though it is not. The change is not inherited and is not present in every cell of the body; it arises in a single blood forming cell and is passed to that cell's descendants. Polycythemia vera is grouped with essential thrombocythemia and myelofibrosis as a myeloproliferative neoplasm, a family of bone marrow cancers defined by overproduction of mature blood cells.
How is it told apart from a secondary rise?
| Polycythemia vera | Secondary polycythemia | |
|---|---|---|
| Cause | A fault in the marrow itself | A response to low oxygen, a hormone producing tumor or certain drugs |
| Erythropoietin level | Low, since the signal is being bypassed | Normal or high, since the signal is what is driving it |
| Other cell lines | Platelets and white cells often raised too | Red cells alone |
| Spleen | Often enlarged | Usually normal |
The hormone level is the most useful single discriminator, and genetic testing of blood for the JAK2 change confirms the diagnosis; a bone marrow aspiration and biopsy add supporting detail.
What does it cause?
Thickened blood produces headache, dizziness, ringing in the ears, blurred vision and a ruddy complexion. Itching after a warm bath or shower is characteristic and can be intensely troublesome. Burning and redness in the hands and feet reflect small vessel obstruction. The spleen enlarges as it takes on extra work, causing fullness on the left side. The serious risk is clotting, in ordinary sites such as the leg veins and lungs and in unusual ones such as the veins draining the liver. Over many years the marrow can become scarred, or the disease can transform into an acute leukemia, which is why it is followed long term.
Also known as
Used in a sentence
Laboratory testing, including analysis for a JAK2 mutation, was ordered to evaluate for polycythemia vera.
Good to know
Polycythemia vera is a primary disorder of the marrow, distinguished from secondary polycythemia, a reactive rise driven by another condition such as chronic low oxygen; the erythropoietin level is low in the first and normal or raised in the second.
Word origin
Where “polycythemia vera” comes from
Formed from poly-, Greek for many, cyt-, from kytos, meaning cell, and -emia, indicating a blood condition, combined with vera, Latin for true, distinguishing this primary disorder from a secondary rise in red blood cell count.