23rd July 2024

Essential thrombocythaemia (ET)

Background of ET

ET is a true primary thrombocytosis that is not a reactive erythrocytosis or due to another MPN or MDS.

Median age at diagnosis is ~60 years with a female predominance.

The precise aetiology is unknown. JAK2 V617F mutations are found in ~50% of ET. Mutually exclusive JAK2, CALR or MPL mutations are found in ~80-90% of ET.

Presentation and diagnosis of ET

Patients are asymptomatic and diagnosis is incidental in ~50% of cases.

Vasomotor symptoms may be the presenting complaint, including headaches, lightheadedness, atypical chest pain, paraesthesia, livedo reticularis and erythromelalgia. Arterial or venous thrombosis and bleeding (mucosal or gastrointestinal) can occur. Aquagenic pruritus is very uncommon.

Splenomegaly may be present on examination.

Diagnostic criteria for ET include:

• Platelets >450 x10⁹/L (with blood film showing marked thrombocytosis with platelet anisocytosis)
• Bone marrow biopsy showing proliferation mainly of the megakaryocytic lineage
• Exclusion of reactive thrombocytosis and other MPNs and MDSs
• Demonstration of JAK2, CALR or MPL mutations

Management and prognosis of ET

Treatment is not curative; aims are to reduce symptoms and risk of complications. Treatment is determined by risk of thrombosis. All patients should be given advice on managing other cardiovascular risk factors.

High risk patients (≥60 years old or history of arterial or venous thrombosis) receive cytoreductive therapy with hydroxycarbamide. Patients with previous venous thrombosis receive anticoagulation and patients with previous arterial thrombosis receive low-dose aspirin.

Intermediate risk patients receive low-dose aspirin ± hydroxycarbamide.

Low risk patients can be monitored with no therapy or receive low-dose aspirin.

Generally, ET is an indolent disease with most patients having a normal life expectancy. Transformation to AML or primary myelofibrosis can occur but is uncommon.