Essential thrombocythemia (ET) is a rare, chronic blood disorder where the bone marrow produces an excessive number of platelets. Platelets are tiny, sticky blood cells that play a primary role in forming blood clots to stop bleeding when blood vessels are injured. In individuals with ET, this overproduction leads to abnormally high platelet counts in the bloodstream. This condition is considered acquired, developing due to genetic changes within certain bone marrow stem cells.
Understanding ET as a Blood Cancer
Essential thrombocythemia is classified as a myeloproliferative neoplasm (MPN), a type of chronic blood cancer. The term “neoplasm” refers to an abnormal growth of cells, meaning the bone marrow produces too many blood cells in an uncontrolled manner. The World Health Organization (WHO) formally recognizes all myeloproliferative neoplasms, including ET, as blood cancers. Despite this classification, ET is often described as a slow-progressing, or “indolent,” cancer. Many individuals with ET experience a stable disease course for extended periods, and it develops very slowly.
Signs and Symptoms
Many individuals with essential thrombocythemia do not experience symptoms at the time of diagnosis, often discovering the condition incidentally during a routine complete blood count (CBC). When symptoms do occur, they can vary widely among patients. Common complaints include persistent headaches, dizziness, and generalized fatigue. Patients may also notice visual changes, such as temporary disturbances or “silent migraines.” A burning, tingling, or prickling sensation in the hands and feet, known as erythromelalgia, is another frequent symptom, sometimes accompanied by redness or swelling in these areas. More serious symptoms relate to the main complications of ET: blood clots and bleeding events. Blood clots, or thrombosis, can manifest as slurred speech, weakness on one side of the body, sudden chest pain, or a painful, swollen, and warm limb. Conversely, some individuals may experience unusual bleeding, such as nosebleeds, bleeding gums, or gastrointestinal bleeding.
The Diagnostic Process
Diagnosis of essential thrombocythemia involves several steps to confirm the condition and distinguish it from other causes of elevated platelet levels, such as inflammation or iron deficiency. Genetic testing is an important step, as specific mutations in genes like JAK2, CALR, or MPL are found in most patients with ET. The presence of one of these mutations is a major diagnostic criterion for ET. A bone marrow biopsy and aspirate are also performed to examine the bone marrow directly. This procedure confirms the overproduction of megakaryocytes, the cells that produce platelets, and assesses for any signs of bone marrow fibrosis or scarring.
Treatment Strategies
Treatment for essential thrombocythemia aims to reduce the risk of serious complications like blood clots and bleeding, while also managing any existing symptoms. The approach is highly individualized, based on a patient’s risk stratification, which considers factors such as age, medical history of blood clots, and current platelet count. For some low-risk patients, a “watch and wait” approach involving careful observation may be sufficient. Low-dose aspirin, typically 81-100 mg daily, is often prescribed to reduce the risk of blood clot formation, especially for those experiencing microvascular symptoms.
For high-risk patients, or those with very high platelet counts, cytoreductive therapies are used to lower platelet levels. Hydroxyurea is a commonly used first-line medication, effective in controlling platelet counts and reducing vascular complications. Anagrelide is another medication that works by interfering with the maturation of megakaryocytes in the bone marrow, thereby decreasing platelet production. Interferons are biological response modifiers that can also lower platelet counts and are sometimes preferred for younger patients or during pregnancy.
Managing Long-Term Health and Potential Risks
Living with essential thrombocythemia involves ongoing monitoring and proactive management to maintain overall health. Regular follow-up appointments with a hematologist are important, typically involving blood tests every three to six months, to monitor platelet counts and assess for any changes in disease activity. The primary long-term risks associated with ET are blood clots (thrombosis) and, less commonly, bleeding events (hemorrhage).
While ET is generally a chronic and stable condition, a small percentage of patients may experience disease progression over many years. This progression can involve the transformation into other more aggressive conditions, such as myelofibrosis, characterized by the scarring of the bone marrow. Additionally, a very small percentage of patients may progress to acute myeloid leukemia (AML), a more serious form of blood cancer.