Essential Thrombocythemia

Aka: Essential Thrombocythemia, Essential Thrombocytosis

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II. Epidemiology

  1. More common in women

III. Findings: Symptoms and signs

  1. Major Hemorrhage (4% in children, 4-8% in adults)
  2. Splenomegaly (54% in children, 12% in adults)
  3. Microvascular symptoms (4 to 27% in children, 29% in adults)
    1. Headache
    2. Paresthesias
    3. Distal extremity vasomotor symptoms or erythromelagia (erythema, warmth and pain)
  4. Thrombosis (3% in children, 19-22% in adults)
    1. Arterial thrombosis (Angina or MI, TIA or CVA, mesenteric thrombosis, CRAO)
    2. Venous thrombosis (DVT, PE, Portal Vein Thrombosis, Cerebral Sinus Thrombosis)
  5. References
    1. Gangat (2024) Blood Cancer J 14(1): 11 [PubMed]
    2. Ianotto (2019) Haemotologica 104(8): 1580-88 [PubMed]

IV. Differential Diagnosis

  1. See Thrombocytosis
  2. Reactive Thrombocytosis
  3. Other Primary Thrombocytosis (e.g. Clonal Thrombocytosis, Chronic myeloproliferative disorder)

V. Labs (rule-out differential diagnosis above)

  1. See Thrombocytosis
  2. C-Reactive Protein (CRP) Normal
  3. Erythrocyte Sedimentation Rate Normal
  4. Fibrinogen Level Normal
  5. Bone Marrow Biopsy Normal

VI. Diagnosis

  1. Major Criteria
    1. Platelet Count >450,000/uL AND
    2. Bone Marrow Biopsy with Megakaryocyte proliferation of major forms AND
    3. NO alternative myeloid neoplasm criteria met
      1. BCR-ABL positive Chronic Myeloid Leukemia
      2. Polycythemia Vera
      3. Primary Myelofibrosis
    4. Positive for gene sequence variations
      1. Janus Kinase 2
      2. Calreticulin
      3. Myeloproliferative Leukemia
  2. Minor Criteria
    1. Clonal markers are present
    2. Reactive Thrombocytosis excluded
  3. Interpretation
    1. Diagnostic criteria met if all 4 major criteria present (or first 3 major, and both minor criteria met)

VII. Management

  1. Medications
    1. Aspirin 81 mg daily
      1. Used for prevention of thrombotic events
      2. Caution in extreme Thrombocytosis (Platelet Count >1,000,000/uL)
        1. Risk of Hemorrhage (due to acquired vov Willebrand syndrome)
    2. Cytoreductive Therapy
      1. Hydroxyurea
        1. First-line agent in intermediate to high risk Essential Thrombocythemia
      2. Other agents
        1. Pegylated Interferon Alfa-2A
        2. Anagrelide
        3. Busulfan
        4. Ruxolitinib (Jakafi)
    3. Thrombocytapheresis
      1. Rare use, but may be indicated in acute Thromboembolism or Hemorrhage
  2. Age Under 60 years
    1. Low risk patients
    2. Consider low dose Aspirin (esp. intermediate and high risk patients)
    3. Other treatments may be considered in high risk patients
  3. High risk patients over age 60 years
    1. Low dose Aspirin
    2. Hydroxyurea
  4. Cohorts
    1. Women of child bearing age
      1. Risk for pregnancy loss and VTE in Pregnancy/postpartum
        1. Pregnancy management team includes OB, MFM and hematology
      2. Consider low dose Aspirin (esp. preconception or during pregnancy)
      3. Avoid Hydroxyurea (Teratogenic, or discontinue at least 3 months before conception)
      4. Interferon alfa in high risk patients
    2. Children and Teens
      1. Avoid medications in asymptomatic patients
      2. Consider low dose Aspirin if symptomatic, or additional risk for thrombosis or cardiovascular events
        1. However, Aspirin in children is associated with Reye Syndrome risk, as well as bleeding complications
      3. Cytoreductive therapy
        1. Avoid outside of high risk patients, or those who fail low dose Aspirin therapy

VIII. Complications

  1. Hematologic complications
    1. Thrombosis risk (see below)
    2. Hemorrhage risk (due to acquired Von Willebrand Syndrome)
  2. Malignancy
    1. Acute Leukemia (2-3% of patients)
    2. Myelofibrosis (7-13% of patients)

IX. Prognosis: Thrombosis Risk (Revised International Prognostic Score)

  1. Very low Thrombosis Risk
    1. No history of thrombosis
    2. Age <=60 years
    3. No JAK2 sequence variation
  2. Low Thrombosis Risk
    1. No history of thrombosis
    2. Age <=60 years
    3. POSITIVE JAK2 sequence variation
  3. Intermediate Thrombosis Risk
    1. No history of thrombosis
    2. Age >=60 years
    3. No JAK2 sequence variation
  4. High Thrombosis Risk
    1. POSITIVE History of thrombosis
    2. Age >=60 years
    3. POSITIVE JAK2 sequence variation
  5. References
    1. Barbui (2015) Blood Cancer J 5(11): e369 [PubMed]

X. Prognosis: Mean Survival (based on AAA+ Risk Model)

  1. Criteria
    1. Score 8: Age >=70 years
    2. Score 2: 50 to 70 years
    3. Score 1: Absolute Neutrophil Count >= 8000/uL
    4. Score 1: Absolute Lymphocyte Count <1700/uL
    5. Score 1: Absolute Monocyte Count >500/uL
    6. Score 1: Male gender
    7. Score 1: Arterial Hypertension
    8. Score 1: Arterial thrombosis
  2. Interpretation (based on total score)
    1. Ultra-Low Risk: 0-1
      1. Median Survival: 42 years
    2. Ultra-Low Risk: 2-4
      1. Median Survival: 23 years
    3. Ultra-Low Risk: 5
      1. Median Survival: 17 years
    4. Ultra-Low Risk: 6-14
      1. Median Survival: 10 years
  3. References
    1. Tefferi (2025) Am J Hematol 100(11): 2017-27 [PubMed]

XI. References

  1. Tefferi (2001) Am J Med 109:146 [PubMed]
  2. Tefferi (2024) Am J Hematol 99(4): 697-718 [PubMed]
  3. Williams (2026) Am Fam Physician 113(4): 332-8 [PubMed]

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