Patients with raised haemoglobin or haematocrit need evaluation for the presence of polycythaemia. The term erythrocytosis should be used when only the red cells are affected, while polycythaemia is preferred for the clonal disorder involving all three haematopoietic cell lines, namely PV. Secondary erythrocytosis is far more common and is usually consequent to increased erythropoietin production. It is important to diagnose PV, as it has a high morbidity and mortality. The diagnostic criteria for PV are complex. Recently, an activating point mutation in the JAK2 gene (JAK2-V617F) has been detected in a majority of PV patients, but is not specific, and needs more evaluation. Patients may present with plethora, thrombosis in arterial or venous circulations, erythromelalgia, pruritus, haemorrhage, splenomegaly, gout, leucocytosis, or thrombocytosis.
Management consists of reducing haematocrit to below 0·45, primarily by venesection. Low-dose aspirin should be administered to all patients unless contraindicated. Cyto-reductive therapy is indicated only if venesection is not tolerated, for high-risk illness, extreme thrombocytosis, and progressive disease. Hydroxycarbamide (previously known as hydroxyurea) is the simplest and most effective medication, being preferred in all except young patients. Interferon is also effective, but is more toxic and inconvenient to use. Anagrelide may be used to control platelet counts, but hydroxycarbamide appears superior. In the very elderly, P or low-dose busulfan has a role because of the convenience, despite a greater risk of leukaemic transformation. With appropriate therapy, survival has improved from an average of two years to more than ten years. Special care is needed during pregnancy, prior to general surgery, and in the management of haemorrhage,
pruritis, and splenomegaly.
