Polycythemia · What Is It, How It Differs from Polycythemia Vera, and More

Primary polycythemia is most commonly caused by an acquired genetic mutation in the Janus kinase 2 (JAK2) gene. The JAK2 gene codes for a non-receptor tyrosine kinase, which is an enzyme that transfers a phosphate group from adenosine triphosphate (ATP) onto another molecule in order to help regulate cell division. When there is a JAK2 mutation, this process can become unregulated. As a result, hematopoietic stem cell division and differentiation is uncontrolled. They may subsequently differentiate into many types of blood cells, primarily RBCs, white blood cells, and platelets. 

On the other hand, secondary polycythemia results by consequence of another underlying condition.  Secondary polycythemia is most commonly associated with low oxygen levels from tissue hypoxia, which can stimulate the kidneys to increase erythropoietin production. Common causes of this hypoxia include high altitudes, chronic obstructive pulmonary disease, and cyanotic heart disease. Additionally, conditions that directly affect the kidney (e.g., renal artery stenosis, renal cysts, and renal tumors) may also cause an increase in erythropoietin production. Side effects of some hormone-related medications, such as erythropoietin analogues, anabolic steroids, and testosterone, can also cause polycythemia. Rarely, tumors, like hepatocellular carcinoma, can secrete erythropoietin, thereby causing polycythemia.

The primary signs and symptoms of polycythemia include fatigue, headaches, dizziness, and episodic blurred vision. Individuals may also experience peripheral tingling, or burning sensations and itching, after taking a hot shower or bath. Other signs and symptoms may include hypertension, mucosal cyanosis, bruising, and petechiae (i.e., pinpoint spots on the skin that are red and flat). Upon palpation of the abdomen, an enlarged spleen or liver may be felt.

Polycythemia is a blood disease characterized by overproduction of red blood cells. There are two types, primary and secondary. Primary polycythemia, or polycythemia vera, is typically caused by an acquired JAK2 mutation. Secondary polycythemia is polycythemia developing secondarily to another condition that causes increased erythropoietin production and hematopoietic stem cell stimulation, such as tissue hypoxia, kidney diseases, and side effects of certain medications. Common signs and symptoms include fatigue, headaches, episodic blurred vision, and dizziness. Diagnosis includes a medical assessment followed by blood tests that confirm an increased RBC count. Treatment includes removing blood through phlebotomy, increasing fluid intake, taking aspirin, and either suppressing bone marrow RBC production or treating the underlying condition.