Bone marrow disorder increases red blood cells
DEAR DOCTOR: I’ve been diagnosed with polycythemia vera, which I understand is very rare. I’m being treated with phlebotomies. Please explain this diagnosis and what science has learned about it.
DEAR READER: To understand polycythemia vera (PV), you must first understand how bone marrow works. The marrow is full of stem cells that eventually become red blood cells (which carry oxygen), platelets (which help the blood to clot) and white blood cells (which fight infection). Initially, however, the stem cells become either lymphoid cells (which develop into lymphocytes, a specific type of white blood cell) or myeloid cells (which develop into red blood cells, platelets or white blood cells that are not lymphocytes). PV occurs when the myeloid cells reproduce preferentially, producing more of their type of cells.
This causes a significant elevation in the number of red blood cells and, to a lesser degree, platelets and white blood cells. The origin of this proliferation is linked to a mutation in the JAK2 gene, which is only occasionally linked to a genetic susceptibility within families. More often than not, it’s a random mutation.
The greatest complications of PV are due to
the increased concentration of red blood cells and platelets within the blood stream. This increases the risk of blood clots, which can lead to strokes, heart attacks and a sudden loss of blood flow to other organs or to the extremities.
One of the more irritating symptoms of PV is itching, which worsens with exposure to warm water. A more troublesome symptom is a burning sensation in the hands or feet due to alterations of blood flow in the small blood vessels in the feet or hands.
Phlebotomy is often necessary to lower the red blood cell count, which significantly decreases the risk of blood clots. Lowdose aspirin can provide benefit too, not only by reducing the chance of clotting, but by reducing the itching of PV. And, for people over 60, or those with a history of clots, the medication hydroxyurea can help by lowering the red and white blood cell and platelet counts.
Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.
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