Primary thrombocythaemia (PT) (also known as essential thrombocythaemia) is a myeloproliferative disorder. It may be complicated by vascular occlusive and haemorrhagic events. This risk can be reduced six-fold by cytoreductive therapy (from 24% for those not given treatment to 3.6% for those receiving hydroxycarbamide). In a study where all patients received hydroxycarbamide, the incidence of major thrombotic events was 5.6%/year
An anti-aggregating agent, such as aspirin, has been shown to reduce/alleviate minor ischaemic symptoms. Therefore, except in patients with haemorrhagic symptoms, peptic ulceration or known side-effects to aspirin, the use of low-dose aspirin (75mg daily taken with food) is appropriate. The use of aspirin is not contra-indicated in patients with PT receiving anticoagulant therapy.
Haematological transitions to acute leukaemia and myelofibrosis may occur in the longer term. The incidence of acute leukaemic transformation in selected patients treated with Hydroxycarbamide is 5-10% over 4-11 years. Whilst cytoreductive agents reduce the incidence of vascular occlusion and haemorrhage, there is a risk that they may enhance leukaemogenic transformation. Their potential to delay myelofibrotic transformation is unknown.