Untreated PV carries a significant risk of thrombotic complications and a further long term risk of transformation into myelofibrosis or less commonly AML. There is also an 4 risk of bleeding notably from peptic ulcers. The aim of treatment is to reduce the risk of thrombotic complications and to prevent progression to myelofibrosis or leukaemia. Current treatments improve the untreated median survival of 18 months to >15 years though some myelosuppressive treatments (notably chlorambucil and 32P) have been associated with an increased risk of AML. Thrombotic complications notably MI, stroke and venous thromboembolism are the most common causes of death. Age and thrombotic history are the most important risk factors.
PV characteristically presents during the proliferative phase when control of erythrocytosis and prevention of thrombotic complications is often an urgent priority. This is often followed by a stable phase of variable (but often short) duration where near normal counts are maintained without therapy due to decreasing proliferative capacity due to early myelofibrosis. This is followed by an advanced or 'spent phase' which is due to extensive myelofibrosis and associated with progressive hepatosplenomegaly and pancytopenia. Incidence 10-15% after 10 years rising to >30% at 20 years; median survival <18 months. The incidence of AML is estimated at 2% in 243 the absence of therapy but is over 14% after myelosuppressive therapy.
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