The term ‘polycythemia’ is derived from two words, poly (many) and cythemia (cells). Strictly speaking, it denotes an increase in the number of all the three formed elements in the blood that is, the red blood cells (RBCs), the white blood cells (WBCs) and the platelets. However, in practice it is used to describe an increase in the number RBCs only.1,2
Types of Polycythemia
Polycythemia may either be true polycythemia (also called erythremia) or a relative polycythemia (also called erythrocytosis).
True polycythemia: There is an actual increase in the volume of the RBCs while in.
Relative polycythemia: Number of RBCs is normal but it appears to have been increased as it occurs during loss of body water (dehydration).
True polycythemia may further be categorized as primary polycythemia (polycythemia vera) and secondary polycythemia. Primary polycythemia (also known as erythremia or Vaquez-Osler disease) occurs due to certain abnormality in the bone marrow itself, where the blood cells are formed while secondary polycythemia may occur due to a variety of other diseases that may indirectly affect the functioning of the bone marrow.1
Cause of Polycythemia
The basic abnormality in this disease lies in the bone marrow where most of the blood cells are produced. This disorder leads to an excessive production of the RBCs, which are then pumped into the circulation. The cause of this disease is not clearly known. Not only RBCs are increased in numberbut also an increase in the number of WBCs and platelets. At times, the RBCs increase due to presence of certain underlying diseases.
Polycythemia lead to a decrease in the oxygen carrying capacity of the blood and hence stimulate the production of the hormone erythropoietin. This hormone in turn acts on the bone marrow and leads to an increase in the RBCs giving rise to secondary polycythemia.
Chronic diseases of the lungs like emphysema and bronchitis, cardiac diseases associated with congestion of the lungs like mitral valve narrowing are some of the causes of secondary polycythemia.
Once the excess cells enter into the circulation from the bone marrow, the body tries to accommodate this large volume in two ways. It leads to an increase in the unit volume of RBCs (i.e. the number of RBCs per liter of the blood) and also leads to an increase in the total blood cell volume. It will also be obvious that the blood thus becomes much thicker and more viscous than normal.
Thus, most of the symptoms arising due to this disease result from the above pathology.1
Signs and Symptoms
Polycythemia vera is primarily a disease of middle and old age groups. Most people affected by the disease are between 40 and 70 years old. Males are affected slightly more often than females. The signs and symptoms are dependent on the severity of the disease and the rate at which the disease develops.
At the onset of the disease there may be vague symptoms like easy fatigability, headaches and dizziness. The headaches may progressively increase in intensity and last longer. Affected individuals complain of a constant ringing sound in the ear and fullness of head. All these symptoms are due to the congestion of blood vessels in the brain.
Rarely, the first symptom may be a stroke, which brings attention to the disease. Other symptoms related to the heart and difficulty in breathing (dyspnea) may be one of the first symptoms to appear.
Bleeding into the skin especially after mild trauma may be sometimes extensive. Problems with vision like blurring and blind spots are sometimes a feature of the disease. This is also the result of bloated blood vessels.2
The diagnosis of polycythemia is based on symptoms noticed by the individual physical examination conducted by the doctor and certain laboratory tests. The typical signs elicited by the doctor include blood-shot eyes, a ruddy complexion and spleen felt by pressing on the abdomen. The liver may also felt enlarges on examination. At other times, the disease may be diagnosed incidentally during a routine blood test.
The laboratory tests advised included certain routine blood tests and estimation of the levels of a hormone known as erythropoietin. The routine blood tests include estimation of hemoglobin (which is increased), number of RBCs (raised), the packed cell volume (also known as PCV, is increased) and the erythrocyte sedimentation rate (ESR). Erythrocyte sedimentation rate is the rate at which the red cells sediment out of the liquid plasma when the blood is allowed to stand undisturbed for some time. The ESR in polycythemia is very low often.
Estimation of the hormone erythropoietin is used to differentiate between primary and secondary polycythemia. This hormone stimulates the bone marrow to produce RBCs. In polycythemia vera, the levels of this hormone are normal as opposed to secondary polycythemia where the level of hormone is invariably increased.2
The treatment of polycythemia vera consists of one of the following modalities.
Most frequently, it involves a procedure known as phlebotomy wherein about 1 pint of blood is let out of the body every other day till the packed cell volume reaches a normal level. This is monitored and later on phlebotomy might be needed every 6 months. The packed cell volume is maintained to 45% in males and 42% in females.
The other cornerstone of treatment is chemotherapy with drugs such as hydroxyurea and busulphan. These drugs however can give rise to other diseases like leukemia (blood cancer) and are hence used with caution and almost invariably in patients over the age of 70 years. Yet another modality of treatment is the use of radioactive phosphorous.
The treatment of secondary polycythemia involves the diagnosis of the primary condition, giving rise to polycythemia and the treatment of the primary condition. The secondary polycythemia resolves once the condition, giving rise to secondary polycythemia is treated.2,3
Polycythemia in Children
Rare instances of polycythemia may be seen in children secondarily to a cardiac disorder such as tetralogy of fallot; and in cases of transposition of the great vessels and atresia of the tricuspid valve. Babies born at high altitude have a high RBC count because of nature’s mechanism to provide adequate oxygenation. At high altitudes, the air is rare and oxygen content is low. Adults living at high altitudes also have a higher RBC count.
Polycythemia may also be seen in newborns when extra RBCs enter the circulation. Some instances where polycythemia is seen in newborn infants include the following:
- A delay in clamping of the cord.
- Twin to twin transfusion syndrome.
- Certain chromosomal abnormalities like trisomy of 13, 18 and 21 chromosomes are sometimes associated with polycythemia.
Treatment involves phlebotomy, removal of excess blood and replacement of the blood volume with fluids.3
1.Robbins Pathologic Basis of Disease. Cotran, Kumar, Robbins (eds). W.B Saunders publications, 4th en.
2.Clinical Hematology in Medical Practice. David Pennington (ed.). CBS Publishers and Distributors. 3rd Reprint.
3.Tefferi A. Polycythemia vera: A comprehensive review and clinical recommendations. Mayo Clin Proc. 2003; 78: 174–194.
Written by: Saptakee sengupta
Date last updated: April 18, 2015