What is thrombocytosis?

Thrombocytosis is a condition in which there is an excessive number of platelets in the blood. Platelets are blood cells in plasma that stop bleeding by sticking together to form a clot. Too many platelets can lead to certain conditions, including stroke, heart attack, or a clot in the blood vessels.

There are two types of thrombocytosis: primary and secondary. Primary thrombocytosis, also known as essential thrombocythemia (or ET), is a disease in which abnormal cells in the bone marrow cause an increase in platelets. The cause is unknown. It is not considered an inherited (family) condition despite the finding of certain gene mutations in the blood or bone marrow.

Secondary thrombocytosis is caused by another condition the patient may be suffering from, such as:

  • Anemia due to iron deficiency
  • Cancer
  • Inflammation or infection
  • Surgery, especially splenectomy (removal of the spleen)

What is the natural history of thrombocytosis?

Secondary thrombocytosis subsides when the underlying process causing the elevated platelet count resolves (treatment of infection, recovery from surgery, etc.). Even though the platelet count is elevated for a short time (or even indefinitely after splenectomy), secondary thrombocytosis does not typically lead to abnormal blood clotting.

Primary thrombocytosis, or essential thrombocythemia, can cause serious bleeding or clotting complications. These can usually be avoided by maintaining good control of the platelet count with medications. After many years, however, bone marrow fibrosis (scarring) can develop. Transformation of the disease to leukemia occurs in a small percentage of patients.

What are the symptoms of thrombocytosis?

Most patients do not have any symptoms of an increased platelet count. When symptoms do appear, they can include skin bruising or bleeding from various areas such as the nose, mouth, and gums, or the stomach and intestinal tract.

Abnormal blood clotting can also occur, leading to stroke, heart attack, and unusual clots in the blood vessels of the abdomen.

Some patients with essential thrombocythemia develop erythromelalgia, causing pain, swelling, and redness of the hands and feet, as well as numbness and tingling.

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