References:
- Brunner & Suddarth’s Textbook of Medical-Surgical Nursing, 15th Edition, ISBN 978-197-51-6103-3, by Janice L. Hinkle, Kerry H. Cheever, and Kristen J. Overbaugh (Ch. 30, [ebook] pp. 2648–2651)
Essential thrombocythemia, also called primary thrombocythemia, is a rare, chronic, Philadelphia chromosome-negative myeloproliferative disorder characterized by an increased production of megakaryocytes. A marked increase in platelet production occurs, with the platelet count consistently greater than 450,000/mm³. The platelet count can exceed 1 to 2 million/mm³. Occasionally, the thrombocythemia (increase in platelets without a known cause) is accompanied by an increase in erythrocytes, leukocytes, or both; however, these cells are not increased to the extent they are in polycythemia vera or myelofibrosis.
The exact underlying cause of essential thrombocythemia is idiopathic (i.e., unknown). Approximately 50% to 60% of patients have the JAK2 gene mutation, and 25% of patients have the CALR gene mutation.
- This disease affects women twice as often as men and tends to occur later in life (median age at diagnosis is 65 to 70 years). Median survival is about 20 to 33 years; overall survival does not differ from the general population. However, survival rates vary based upon the type of gene mutation present. For example, patients with the CALR mutation have fewer thrombotic events and higher survival rates compared to those with the JAK2 mutation.
Clinical Manifestations
Many patients with essential thrombocythemia are asymptomatic; the illness is frequently diagnosed as the result of an incidental finding of an elevated platelet count on a CBC. Symptoms occur most often when the platelet count exceeds 1 million/mm³; however, they do not always correlate with the extent to which the platelet count is elevated. When symptoms do occur, they primarily result from vascular occlusion.
- This occlusion can occur in large arterial vessels (cerebrovascular, coronary, or peripheral arteries) and deep veins, as well as in the microcirculation; inflammation that may occur in the vascular endothelium may result in erythromelalgia. More common forms of venous thromboembolism (VTE), including DVT and pulmonary embolism (PE), can also occur.
One of the most common neurologic symptoms of essential thrombocythemia is headaches. Other neurologic manifestations that may be related to compromised blood flow include dizziness; lightheadedness; paresthesias; visual changes, such as diplopia; and TIAs. Other symptoms can include tinnitus and chest pain.
Because the platelets can be dysfunctional, minor or major hemorrhage may occur. Bleeding is commonly limited to recurrent minor manifestations (e.g., ecchymoses, hematomas, epistaxis, gum bleeding), although significant GI bleeding and intracranial hemorrhage are both possible and considered major hemorrhagic events. Bleeding typically does not occur unless the platelet count exceeds 1.5 million/mm³. It results from a deficiency in von Willebrand factor as the platelet count increases (vWF binds to platelets).
Assessment and Diagnostic Findings
Essential thrombocythemia, by definition, is diagnosed when other causes for thrombocythemia have been ruled out, e.g., other myeloproliferative disorders or underlying illnesses.
- Iron deficiency should be excluded, because a reactive increase in the platelet count often accompanies this deficiency.
The diagnosis is typically based upon both an evaluation of clinical manifestations and laboratory findings.
- The CBC will show markedly enlarged and abnormal platelets, as well as a persistently elevated platelet count (greater than 450,000/mm³).
- A bone marrow examination (i.e., aspirate or biopsy) can help distinguish between true essential thrombocythemia and other myelofibrotic diseases.
Complications
Complications include inappropriate formation of thrombi and hemorrhage. Cause of death in patients is often the result of thrombosis or major bleeding (collectively called thrombohemorrhagic events) or transformation to AML or myelofibrosis.
- Patients with cardiovascular risk factors (e.g., obesity, smoking, and poorly controlled hypertension, diabetes, hyperlipidemia) are at higher risk for thrombotic complications.
- Patients older than 60 years and those with a history of prior thrombosis are at higher risk for complications.
- Major bleeding tends to occur when the platelet count is very high (greater than 1.5 million/mm³) and there is a prior history of major bleeding.
Medical Management
The goals of management are to minimize the risk of thrombohemorrhagic events and to control symptoms. Treatment for essential thrombocythemia is based upon a patient’s risk stratification.
- Patients at low risk are less than 60 years of age, without the JAK2 mutation, and without a prior history of thrombosis. Typical treatment for these patients includes:
- Ongoing monitoring for new thrombosis and acquired von Willebrand factor deficiency and disease-related major bleeding;
- Management of cardiovascular risk factors, e.g., obesity, smoking, and poorly controlled hypertension, diabetes, or hyperlipidemia; and
- Daily low-dose aspirin as long as the patient remains asymptomatic.
- Patients are at high risk when there is a history of thrombosis at any age or is age 60 or older or with the JAK2 mutation.
- Besides use of aspirin, treatment may also include prescribing hydroxyurea, interferon-alfa, or anagrelide (cytoreductive agents, discussed in polycythemia vera), all of which are effective in decreasing platelet counts to a level below 400,000/mm³ and reducing risk for developing arterial thrombosis and hemorrhage. However, the side effects of these agents may be intolerable. As previously noted, anagrelide has been associated with disease progression to myelofibrosis or AML.
Patients who develop arterial or venous thrombosis require additional treatment. Anticoagulant therapy may be useful for patients with active thrombosis and platelet apheresis (removal of platelets from the bloodstream) may be used in patients with acute life-threatening thrombosis or major bleeding.
Nursing Management
It is important to assess patients for a history of prior thrombohemorrhagic events, because these are the primary cause of morbidity and mortality.
- Patients with essential thrombocythemia should be educated on signs and symptoms of hemorrhage and thrombosis, particularly the neurologic manifestations, such as visual changes, numbness, tingling, and weakness.
- Patients should be encouraged about medication adherence and management of side effects.
- In particular, patients taking aspirin should be informed about the importance of taking this medication as well as the increased risk of bleeding.
- Those patients taking hydroxyurea should have their CBCs monitored regularly; the dosage is adjusted based on the platelet and WBC count.
- Patients taking interferon-alfa may be taught to self-administer the medication and how to manage its side effects.
- Cardiovascular risk factors associated with thrombotic complications should be assessed, such as obesity, smoking, and poorly controlled hypertension, diabetes, or hyperlipidemia. Measures should be identified and encouraged to reduce these risks.
- Additionally, patients who are at risk for bleeding should be educated about medications (e.g., aspirin, nonsteroidal anti-inflammatory agents [NSAIDs]) and other substances (e.g., alcohol, certain herbal therapies) that can alter platelet function.