Overview

Also known as primary thrombocytosis and thrombocythaemia, essential thrombocytosis (ET) is a myeloproliferative disorder characterised by excessive megakaryocyte proliferation and production of platelets. This occurs as the platelet precursors are more sensitive to growth factors.

ET can progress to secondary myelofibrosis (MF). Around 60% of patients with ET have a mutation in JAK2.

Epidemiology

  • The most common type of myeloproliferative neoplasm
  • Prevalence is around 50 per 100,000
  • Incidence highest in >50 years of age
  • More common in females

Risk Factors

  • Not many risk factors are known
  • JAK2 mutation

Presentation

Patients have arterial and venous thrombosis. Features are:

  • Erythromelalgia – burning and/or redness of the fingers/hands/heels/toes :
    • Due to thrombi forming in the blood vessels of the extremities
  • Splenomegaly:
    • Due to the increased sequestration of cells
    • This can lead to splenic infarction and hyposplenism
  • Arterial and venous thrombosis e.g. stroke, myocardial infarction, pulmonary embolism etc.
  • Livedo reticularis – purple mottled discolouration of the skin:
    • Usually seen on the legs
    • Due to small thrombi in cutaneous capillaries
  • Some patients are asymptomatic

Differential Diagnoses

Secondary (reactive) thrombocytosis

  • This can be due to inflammation, infection, malignancy, hyposplenism, ulcerative colitis, etc.
  • Inflammatory markers such as erythrocyte sedimentation rate and/or C-reactive protein may be raised
  • Iron deficiency may be seen, which can cause thrombocytosis

Investigations

All patients

  • Full blood count (FBC) and white cell differential:
    • Thrombocytosis is seen – raised platelets
  • Blood film:
    • Immature platelet precursor cells may be seen
    • Howell-Jolly bodies may be seen if hyposplenism is present
  • Iron studies:
    • To screen for other secondary causes of thrombocytosis – iron deficiency can cause thrombocytosis
  • Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
    • Normal in ET – used to screen for secondary causes of thrombocytosis
  • Bone marrow biopsy:
    • Diagnostic test – shows proliferation of the megakaryocyte lineage
  • JAK2 mutation screen:
    • May be positive

Management

All patients

  • Low-dose aspirin is often used to reduce the risk of thrombotic events
  • Hydroxyurea is often used
  • Anticoagulation is considered in some patients

Complications

  • Transformation to myelofibrosis
  • Transformation to acute myeloid leukaemia (AML)
  • Arterial and venous thrombosis
  • Spontaneous abortion
  • Recurrent miscarriages

Prognosis

  • Life expectancy is reduced due to the risk of thrombotic events and the risk of transformation

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