Polycythemia vera

Polycythemia vera is a blood disorder where the bone marrow abnormally increase the production of blood cells, especially red blood cells (RBCs).

Even though this disorder causes a significant increase in the count of red blood cells (polyglobulia), it may also increase the count of leukocytes or white blood cells (leukocytosis) and platelets (thrombocytosis). The first sign is the increase in the number of red blood cells in a blood test and consequently the blood is thicker (more viscous) than normal.

Polycythemia vera is classified as a myeloproliferative neoplasm or a chronic myeloproliferative disorder.

Polycythemia vera is a genetic disease related to a mutation of the JAK2 (Janus kinase 2) gene located on chromosome 9.

This genetic mutation leads to an excessive production of blood cells that is not dependent on erythropoietin.

Polycythemia vera often appears in people over 40 years old. It is more common in men than in women (3 cases per 100,000 population of men and 1 case per 100,000 population of women, approximately).

Polycythemia vera is a slow-growing blood cancer. The symptoms related are usually very common and not very specific:

• Fatigue
• Dizziness
• Tinnitus (ringing in the ears)
• Headache
• Visual disturbances
• High blood pressure
• Vertigo
• Paresthesia (numbness and tingling sensation in the extremities)

The most characteristic symptom is aquagenic pruritus, intense itching after contact with water.

As the disease progresses, some patients may experience that the face becomes red and warm (flushed), mainly in the ears, nose, or cheeks.

It is a difficult disorder to diagnose. It is usually suspected after a blood test performed for another reason that shows an unnoticed increase in the number of red blood cells, hemoglobin, and hematocrit with no apparent cause.

The following causes should be ruled out:

• Living at high altitudes
• Heavy smoker
• Heart or lung disease
• Kidney or neurological diseases: where there may be an increased production of erythropoietin, a hormone that stimulates the synthesis of red blood cells
• Drug interference (diuretic, corticosteroid)

The major criteria for the diagnosis of polycythemia vera are the following ones:

• Total red blood cell mass greater than 36 ml/kg in men and 32 ml/kg in women
• Normal arterial oxygen saturation level and decreased erythropoietin (EPO) level in the blood (it is a sign that the increase in the red blood cell count is not secondary to hypoxia or lack of oxygen supply)
• Splenomegaly (enlarged spleen)
• Increase in white blood cell count (greater than 12,000 per ml of blood) and/or platelets (greater than 400,000 per ml of blood).

Currently, a JAK2 mutation test can also be performed to detect the mutation in the JAK2 gene.

Polycythemia vera is a chronic disorder and there is no cure for it. However, treatments can help control the disease.

Some drugs often used are antineoplastic drugs such as hydroxycarbamide or hydroxyurea. These drugs help reduce the red blood cell count. As an alternative, Jakafi (Ruxolitinib) can be used in case of inadequate response or resistance to hydroxyurea.

Periodic phlebotomies (also called venipuncture) can also be performed. Phlebotomy is a technique performed to drawing blood from a vein using a needle. This technique helps reduce the thickness of the blood and reduce the hematocrit concentration (the percentage of red blood cells in the blood).

Finally, daily doses of 100 mg of aspirin (acetylsalicylic acid) are usually recommended to reduce the risk of blood clots.

Currently, polycythemia vera has an average of 15 to 20 year survival rate, but many patients may live much longer.

The most important complication of polycythemia vera is the progression over the years towards myelofibrosis or acute myeloid leukemia.