What is polycythemia vera and Types of polycythemia and their causes?

Polycythemia is a blood disorder in which the bone marrow produces too many red blood cells, causing headaches, weakness, and itching. Know its causes and what its treatment is.

Polycythemia is a disease characterized by an increase in the blood of the number of red blood cells. There is a primary form (polycythemia vera), which presents an uncontrolled proliferation of red blood cells, white blood cells, platelets, and a secondary structure. Only the red blood cells are increased in number and volume.

The polycythemia vera was first described in 1892 by Vaquez. The main symptoms have been weakness, prostration, constipation, headache, and vertigo”. For this reason, polycythemia vera is also called Vaquez-Osler disease.

Polycythemia generally has an insidious onset, most common during the sixth decade of life, although it can also begin in infancy or old age. Presenting symptoms include headache, facial flushing, itching, thrombosis, and gastrointestinal bleeding, but some patients are diagnosed because alterations are found in the results of a simple laboratory test. At least 30% of patients with polycythemia are symptoms reported by more to less frequent headache, weakness, itching, dizziness, and sweating.

Polycythemia vera is a disease compatible with standard or almost normal life for many years. However, eventually, patients can develop leukemia, which is slightly more common in people who have received specific treatments. Thrombosis is the most common cause of death in those affected (30% of deaths), followed by acute leukemia (19%), other cancers (15%), and bleeding (5%).

Types of polycythemia and their causes

Although there is no single cause of polycythemia vera, it is known that there are several factors that contribute to the abnormal production of red blood cells, which would be the origin of this blood disorder: 

  • Increased sensitivity to erythropoietin. Red blood cell precursor cells are more sensitive to the stimulus generated by erythropoietin to form erythrocytes or red blood cells.
  • Chromosomal alterations. In a variable percentage of patients with polycythemia, vera abnormalities are detected in chromosomes 8, 9, 17, and 20 that could explain this disease. In chromosome 9, there is a specific mutation of the JAK2 gene, which has recently been used as the most determining factor for the development of this disease. It is estimated that more than 90% of them express this mutation as a cause of polycythemia vera.
  • Endogenous red blood cell formation.

Types of polycythemia vera

Polycythemia is characterized by an increase in the blood of the number of red blood cells, and there are two types of polycythemia :

Primary polycythemia or polycythemia vera: it is an alteration of the hematopoietic stem cell (precursor cell that gives rise to different blood cells), characterized by an uncontrolled proliferation of blood cells (white blood cells, red blood cells, and platelets). Although the predominance of red blood cells is the characteristic feature of the disease, an increase in white blood cells and platelets is also common.

The causes of the malignant transformation that occurs in polycythemia vera are unknown. The description in 2005 of an acquired mutation of the JAK2 gene in more than 90% of those affected by polycythemia vera has allowed a better understanding of the disease. Its incidence is 0.7-2.6 cases per 100,000 people per year, and it is slightly more frequent in men, mainly affecting people between 50 and 70 years of age. It is rare before the age of 40 (4% of cases).

Secondary polycythemia or secondary erythrocytosis: refers to those situations in which only the red blood cells increase. In turn, secondary polycythemia can be subdivided into:

  • Appropriate polycythemia: an increase in the number of red blood cells occurs in response to hypoxia (low oxygen in the blood). Such additions can be seen, for example, in people who reside at high altitudes, in people who smoke heavily, and in patients with cardiopulmonary disease.
  • Inappropriate polycythemia – Red blood cell formation (erythropoiesis) is stimulated by abnormal erythropoietin (EPO) production. This occurs, for example, in people with inherited diseases or tumors.