What are the similarities between polycythemia and erythrocytosis?

Polycythemia and erythrocytosis, both lead to an increase in erythrocytes or red blood cells in the body. Both conditions are affected by genetics as well as smoking and high altitudes. Both conditions manifest similar symptoms, which may include headaches, dizziness, high blood pressure, and nausea. The treatment – phlebotomy – is the same for both conditions.