[The polycythemias].

The primary polycythemias result from malignant proliferation of myeloid stem-cell. Typically, an increase of red cell mass and a decrease of erythropoietin is found. In polycythemia vera, augmentation of PCV is frequently associated with elevation of WBC and platelets, as well as splenomegaly. The treatment consists of venosection and administration of P32 or cytostatics; all of which methods exhibit a specific risk. In secondary polycythemias, augmentation of red cell mass is consecutive to increased erythropoietin production; these hypererythropoietinemias may be induced by hypoxia or, rarely, may result from an inappropriate tumoral (malignant or benign) secretion. "Spurious" polycythemias are finally defined by the more or less normal red cell mass. They are divided into three groups: micropolycythemias, relative polycythemias and "spurious" chronic polycythemias. The latter are frequent and exhibit relatively important morbidity and mortality, and therefore the recently proposed new therapeutic approaches should be considered. Tobacco addiction appears to be one of the major causes of these "spurious" polycythemias.