History and exam

Key diagnostic factors

common

erythromelalgia

Common vasomotor manifestation characterised by burning pain and dusky congestion of the extremities. The pain of erythromelalgia increases with exposure to heat and improves with cold.

splenomegaly

Present in approximately 10% to 20% of essential thrombocythaemia patients at diagnosis, and is usually modest in degree.[8][9]​​

arterial and venous thrombosis

Common complication in people who are symptomatic. Thrombotic events may include stroke, transient ischaemic attacks (TIAs), retinal artery or venous occlusions, coronary artery occlusion, pulmonary embolism, hepatic or portal vein thrombosis, deep vein thrombosis, and digital ischaemia.[6]​

Digital ischaemia may initially manifest as Raynaud's phenomenon with pallor and/or cyanosis of the digits, but may progress to ischaemic necrosis of the terminal phalanges.

Patients with TIA should undergo carotid ultrasound to rule out carotid artery stenosis.

bleeding

Common complication in people who are symptomatic.

Bleeding events are usually mild and manifest as epistaxis or easy bruising. The gastrointestinal tract is the most common site of major bleeding.[7]

Increased risk of bleeding is associated with extreme thrombocytosis (platelet count >1000 × 10⁹/L [>1 million/microlitre]) and use of aspirin in doses of >325 mg/day.[35]

livedo reticularis

Characterised by a purplish mottled discoloration of the skin, usually on the legs. This discoloration is typically described as lacy or net-like in appearance. Livedo reticularis may occur in essential thrombocythaemia, but is also seen in several connective tissue diseases (e.g., lupus, antiphospholipid syndrome, Sneddon's syndrome). It may also be an adverse effect of cytoreductive therapy with hydroxycarbamide.

Other diagnostic factors

common

age ≥60 years

Essential thrombocythaemia more commonly affects older people (approximately 66% of patients in the US are age ≥60 years at diagnosis).[12]

Median age at diagnosis is 67 years in the US, and 72 years in the UK.[12][14]​​

Younger people may develop the disease.

female sex

Essential thrombocythaemia occurs more commonly in females (male to female rate ratio approximately 0.8).[12][14]​​​

headache

The most common neurological symptom.

dizziness, lightheadedness, chest pain, vertigo, and paraesthesia

Common vasomotor symptoms.

uncommon

syncope and seizures

Uncommon vasomotor manifestation.

transient visual disturbances

Uncommon vasomotor manifestation.

priapism

Rare complication related to corpus cavernosum thrombosis.

Risk factors

weak

genetic mutations (JAK2 V617F, CALR, or MPL)

Driver mutations can cause abnormal blood cells to grow and proliferate uncontrollably.

The JAK2 V617F, CALR, and MPL mutations are present in approximately 50% to 60%, 25% to 30%, and 3% to 11% of patients with essential thrombocythaemia (ET), respectively.[19]​ Approximately 10% to 15% of patients with ET are negative for all three driver mutations (triple‐negative); therefore, absence of these mutations does not exclude the diagnosis.[19]​

Driver mutation expression is often considered to be mutually exclusive in ET; however, there are reports of patients with coexisting JAK2 V617F and CALR, or JAK2 V617F and MPL, mutations.[20][21]​

black ethnicity

Incidence of essential thrombocythaemia is highest among black people in the US.[12]

age ≥60 years

Essential thrombocythaemia more commonly affects older people (approximately 66% of patients in the US are age ≥60 years at diagnosis).[12]

Median age at diagnosis is 67 years in the US, and 72 years in the UK.[12][14]​​

Younger people may develop the disease.

female sex

Essential thrombocythaemia occurs more commonly in females (male to female rate ratio approximately 0.8).[12][14]​​​

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