A CLInICAL APPROACH TO POLyCyTHEMIA

Polycythemia literally means too many cells in the blood and is initially classified into relative and absolute. In absolute polycythemia the red cell mass is increased where as in relative it is not. Since automated blood counts are done commonly many asymptomatic patients with polycythemia are detected. Hematocrit value above 51% for males and 48% for females requires further evaluation. Values above 60% in males and 55% n females almost establish absolute polycythemia. Absolute polycythemia is classified into primary and secondary. The most important cause of primary polycythemia is PV a clonal disorder of hemopoietic stem cell which shows selective growth advantage (erythroid cell line). Recently JAK2 mutation has been discovered in majority of patients with PV. Important secondary causes are smoking, chronic lung disease, renal and hepatic tumours and high attitude. Chuvash polycythemia is a hereditary polycythemia found in Chuvash population of the Russian republic. It is a primary polycythemia but also has features of secondary variety (the Epo level is increased) More information is now available regarding EPO receptors, HIF (Hypoxia inducible factor), O 2 sensor and increased 0 2 affinity. It is very important to differentiate PV (the most important form of primary polycythemia) from secondary causes by appropriate investigations. The diagnosis of PV is made easier with the new revised criteria (WHO 2008). The complications of polycythemia are an increased risk of thrombosis and hemorrhage. Thrombosis may occur at unusual sites like hepatic veins producing Bud Chiari syndrome. PV after many years of proliferative phase passes into a spent phase (post polycythemia myeloid metaplasia PPMM) and a phase of acute leukaemia. The basic treatment of polycythemia is to control the hematocrit to 45% in males and 42% in females by phlebotomy. Secondary causes of polycythemia should be appropriately treated. PV is currently treated according to the risk category. Myelosuppressive drugs like hydroxyurea should be added to PV to control the elevated WBC and platelet counts. Low dose of aspirin is useful. Treatment of PV during the PPMM and the leukaemia is not satisfactory. Pregnant women with PV require special care as the incidence of foetal wastage is very high. Future is bright as targeted therapy may be researched and may be used up front.