Canterbury DHB
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About 150 people in Christchurch have essential thrombocythaemia, which is a myeloproliferative disorder found typically in middle aged adults. It is commonly diagnosed incidentally in a person with a sustained raised platelet count, not secondary to any other cause such as inflammation or infection. The principal problem seen is an increased incidence of arterial and venous thromboses. Patients may continue with this chronic disorder for decades, and remain well. Occasional patients may progress to develop other related haematological disorders such as acute leukaemia or myelofibrosis.
In patients with essential thrombocythaemia, those at highest risk of thrombosis have any of the following:
There is an evidence based case that such patients should be treated with hydroxyurea to achieve as near as normal full blood count as possible.
Patients are at low risk of thrombosis if they are:
These patients should not be treated with hydroxyurea.
If patients are not at high risk or low risk, they are at intermediate risk. We don’t know whether these patients benefit or not from treatment, and some patients are participating in a randomised trial to clarify this.
If there are no contraindications, all patients are advised to take aspirin 100 mg daily.
Hydroxyurea is presented in capsules containing 500 mg. Patients typically take between 500 mg - 1500 mg daily in a single dose in the morning. The drug is usually well tolerated and patients do not typically have side effects of nausea or alopecia. Macrocytosis is usual. The principal side effect is excessive myelosuppression, so the blood count should be monitored at intervals to check it remains near normal, and in particular that platelets are < 600 x 109/L. A typical monitoring interval in a stable patient is two monthly. Hydroxyurea dose often remains stable over many years and often only small changes are necessary, for example from one 500 mg tablet daily to one daily but two on Monday and Thursday. Occasional patients can get atypical skin reactions, particularly painful ulcers in the lower parts of the leg. Such patients cannot continue with hydroxyurea and require a second line treatment.
This is suitable for patients who are well and are either on no treatment or who have been stabilised on hydroxyurea. It resembles a treatment plan for patients with other chronic disorders such as hypertension or diabetes and to the monitoring of treatments such as anticoagulation. The principal difference is that each general practitioner may only have one or two patients with essential thrombocythaemia. The aim of treatment is to maintain the patient in good health, reducing the risk of thrombosis by myelosuppression using hydroxyurea if appropriate. Patients will be reviewed as necessary and at least yearly by a haematologist. At other times they will remain under the care of their primary care physician. If the patient is on treatment with hydroxyurea, this will be monitored and prescribed by their primary care physician. If the patient is well, appropriate monitoring would usually be by the patient having a blood test and the result of the blood test then being compared to previous results, with advice being given (perhaps by phone) about whether there is any need for a change in dose. The patient’s haematologist would usually be consulted if anything unexpected occurred or there were any uncertainty.
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Topic Code: 31427
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