Hematology · Myeloproliferative Neoplasms
The facts most likely to be tested
Essential thrombocythemia is a myeloproliferative neoplasm characterized by a sustained platelet count ≥ 450,000/μL in the absence of other causes of reactive thrombocytosis.
The most common genetic mutation associated with essential thrombocythemia is the JAK2 V617F mutation, found in approximately 50-60% of patients.
Patients frequently present with vasomotor symptoms such as erythromelalgia, which manifests as burning pain and erythema of the hands and feet.
Physical examination often reveals splenomegaly, although many patients remain asymptomatic and are diagnosed incidentally via routine complete blood count.
The primary clinical goal in high-risk patients is the prevention of thrombotic and hemorrhagic complications using low-dose aspirin and cytoreductive therapy.
Hydroxyurea is the first-line cytoreductive agent used to reduce the risk of thrombosis in high-risk patients, defined by age >60 or a history of thrombosis.
Bone marrow biopsy typically shows hypercellularity with an increased number of enlarged, mature megakaryocytes with hyperlobulated nuclei.
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A 65-year-old male presents to the clinic for a follow-up of persistent thrombocytosis noted on a routine physical. He reports occasional burning pain and redness in his feet that improves with cooling. Physical exam is significant for a palpable splenomegaly 2 cm below the left costal margin. Laboratory studies reveal a platelet count of 850,000/μL, hemoglobin of 14.2 g/dL, and a white blood cell count of 11,000/μL. Peripheral blood smear shows large, abnormal platelets.
What is the most appropriate initial pharmacologic management to reduce the risk of thrombotic events in this patient?
Hydroxyurea
This patient is classified as high-risk due to his age (>60) and presence of symptoms, necessitating cytoreductive therapy with hydroxyurea to prevent thrombotic complications.
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Etiology / Epidemiology
Myeloproliferative neoplasm occurring primarily in adults >60 years. Associated with JAK2 mutation in 50-60% of cases.
Clinical Manifestations
Often asymptomatic; presents with erythromelalgia, thrombosis, or bleeding due to platelet dysfunction.
Diagnosis
Diagnosis requires bone marrow biopsy showing megakaryocytic hyperplasia and platelet count >450,000/µL.
Treatment
Hydroxyurea is the first-line cytoreductive therapy for high-risk patients. Avoid in pregnancy.
Prognosis
Risk of thrombotic events is the primary cause of morbidity. Low risk of transformation to acute myeloid leukemia.
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Epidemiology & Etiology
Essential thrombocythemia (ET) is a clonal stem cell disorder most common in patients over 60. It is characterized by the overproduction of platelets. The JAK2 V617F mutation is the most frequent genetic driver, followed by CALR and MPL mutations.
Pertinent Anatomy
The disease originates in the bone marrow hematopoietic stem cells. Overproduction of megakaryocytes leads to sustained peripheral thrombocytosis. The spleen may become enlarged due to extramedullary hematopoiesis.
Pathophysiology
Constitutive activation of the JAK-STAT signaling pathway leads to uncontrolled megakaryocyte proliferation. Excess platelets often exhibit functional defects, paradoxically increasing both thrombotic and hemorrhagic risk. Chronic inflammation and cytokine release contribute to systemic symptoms.
Clinical Manifestations
Patients frequently present with erythromelalgia—burning pain and redness in the hands and feet. Red flag symptoms include arterial or venous thrombosis (e.g., DVT, PE, stroke) and mucosal bleeding. Splenomegaly is found in approximately 20-30% of patients.
Diagnosis
The WHO diagnostic criteria require a platelet count ≥450,000/µL. A bone marrow biopsy is the gold standard, demonstrating increased, enlarged, mature megakaryocytes. Testing for JAK2, CALR, or MPL mutations is mandatory to confirm clonal origin.
Treatment
Low-risk patients (age <60, no prior thrombosis) are managed with low-dose aspirin. High-risk patients require hydroxyurea to reduce platelet counts. Anagrelide is a second-line alternative. Interferon-alpha is the preferred agent during pregnancy.
Prognosis
The primary cause of death is thrombotic complications. Long-term monitoring is required for potential progression to myelofibrosis or acute myeloid leukemia.
Differential Diagnosis
Reactive thrombocytosis: usually secondary to infection, iron deficiency, or inflammation
Polycythemia vera: elevated hemoglobin/hematocrit in addition to thrombocytosis
Primary myelofibrosis: presence of teardrop cells and marrow fibrosis
Chronic myeloid leukemia: presence of the Philadelphia chromosome (BCR-ABL)
Iron deficiency anemia: often causes a reactive increase in platelet count