Polycythaemia vera (PV) is an overproduction of mature red blood cells due to a clonal proliferation in the bone marrow. Myeloid precursors and megakaryocytes may also be increased.
5 per 1,000,000 population.
Most commonly presents over the age of 50 years.
Idiopathic disorder, although genetic and environmental factors have been suggested.
There is clonal expansion of a pluripotent stem cell capable of differentiating into red blood cells, granulocytes and platelets. Erythroid precursors in PV are very sensitive to erythropoietin leading to increased red blood cell production. Polycythemia results in increased blood viscosity increasing the risk of arterial or venous thrombosis. Platelet function is often disrupted risking bleeding.
Patients may be asymptomatic and the diagnosis made on incidental full blood count. Patients may complain of pruritus especially after a hot bath or shower. Hyperviscosity may result in headache or blurred vision. On examination patients may appear plethoric and have splenomegaly or hepatomegaly.
Thrombosis may result in ulceration or gangrene of extremities, myocardial infarction, deep vein throm bosis, transient ischaemic attacks and stroke.
Abnormalities in platelet function can lead to epistaxis, bruising and mucosal bleeding (including peptic ulcer disease) although severe bleeding is unusual.
Increased blood cell turnover can lead to hyper uricemia and gout.
Full blood count shows an increased red blood cell count, haemoglobin and packed cell volume. The whole blood viscosity is raised although plasma viscosity is normal. Polycythaemia vera can be distinguished from other causes of polycythaemia by an increase in white cell count, platelets and a high neutrophil alkaline phosphatase.
Treatment is aimed at maintaining a normal blood count (PCV below 45%) and prevention of the associated complications.
Venesection may be of benefit in treating symptoms but has not been shown to reduce complications. It induces iron deficiency and reduces whole blood viscosity but may increase the platelet count.
Cytotoxic therapy is avoided if possible due to increased risk of acute myeloid leukaemia. Although hydroxyurea has been considered safe for long-term maintenance it is also associated with increased risk of development of leukaemia in comparison with venesection.
Newer therapies under evaluation include α interferon, venesection with low doses of aspirin and anagrelide (for treatment of associated thrombo-cythaemia).
The median survival is 10–20 years with treatment. 10% of patients develop myelofibrosis on average 10 years af-ter diagnosis with polycythaemia vera. 3% of patients treated with venesection only develop acute myeloid leukaemia.