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Essential thrombocythemia


Essential thrombocythemia (ET) is a disorder of the bone marrow characterized by an overproduction of platelets (thrombocytes).Under normal circumstances, the number of thrombocytes is between 150 thousand and 450 thousand per µl of blood. This value may increase to over one million per µl of blood in ET patients. This overproduction of platelets can lead to an increased risk of blood clots (thrombus) and bleeding (hemorrhage). However, with a successful treatment, most patients with ET have a near normal life expectancy.

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Cause

“Essential” means that there are no recognisable causes behind the increase in thrombocytes. The cause of Essential thrombocythemia is still unknown. A number of studies from Italy have shown that, among other factors, a higher exposure to pesticides may increase the risk of farmers developing ET.It is thanks to a Vienna-based research group (R. Kravolics) that we are able to link mutations in our genes directly to ET. Approximately 40 to 50 percent of ET patients demonstrate a genetic mutation (aberration) in the Janus kinase coding (JAK2), followed by around 40 percent with a change in the formation of the protein calreticulin (CALR). The quantitative recording of these genetic mutations gives the attending physician the possibility to record the success of a course of treatment.

Symptoms

Many patients with essential thrombocythemia (ET) remain symptom-free for a long time. Consequently, ET is diagnosed by chance in the course of a routine check-up in most cases. If symptoms do occur, they take the form of tingling sensations in the hands and feet, dizziness, headaches and/or visual impairments. In cases where the thrombocyte count is particularly high (greater than one million per µl of blood), they may well result in bleeding on the skin or mucus membranes.

The role of blood platelets

Blood platelets play an important role in the formation of blood clots. Symptoms of the disease can either be confirmed by a very high platelets count or, in other cases, by means of the functions they are performing. A high number of dysfunctional platelets circulating through the blood stream can lead to bleeding, while a high number of normal platelets increase the risk of blood clots. 

Bleeding and impairment of the microcirculation

Bleeding occurs mostly in the form of nose and gum bleeding, but can also happen in the stomach and intestinal areas as well as through the skin.
When blood clots begin to form in the thinnest vessels, the supply of blood to the affected tissue will become restricted. This occurs in around half of the patients and is noticeable in the fingers and toes through a reddening of the skin, which is accompanied by swelling (erythromelalgia) and a burning and tingling sensation. In the central nervous system, it manifests itself in the guise of functional disturbances such as repetitive sight and speech disorders, dizziness, balance difficulties, paralysis and even seizures.

Possible complications

The most common complications that arise with essential thrombocythemia are blood clots (thrombosis) in the venous or arterial system (infarctions).  They can occur in the large vessels of the upper abdomen (portal vein, hepatic veins, splenic veins, mesenteric veins) as well as in the coronary arteries and in the arteries that serve the brain.
The overall condition of the blood vessels also plays a decisive role in blood coagulation. Hence, the older the person the higher the risk.


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