Difference Between Polycythemia and Polycythemia Vera

Polycythemia is defined as an increase in red cell count, hemoglobin, and PCV. This condition can be due to different causes. When a patient gets polycythemia as a sequel to an underlying disease condition, it is known as secondary polycythemia. On the other hand, polycythemia due to a primary derangement in the physiological mechanisms responsible for the synthesis of hemoglobin is known as primary polycythemia. Polycythemia vera is the commonest cause of primary polycythemia, and it is defined as a clonal stem cell disorder in which there is an alteration in the pluripotent progenitor cell leading to an excessive proliferation of erythroid, myeloid and megakaryocytic progenitor cells. The key difference between polycythemia and polycythemia vera is that polycythemia is the increase in red cell count, hemoglobin, and PCV while polycythemia vera is one of the causes of polycythemia.

CONTENTS

1. Overview and Key Difference
2. What is Polycythemia 
3. What is Polycythemia Vera
4. Similarities Between Polycythemia and Polycythemia Vera
5. Side by Side Comparison –Polycythemia vs Polycythemia Vera  in Tabular Form
6. Summary

What is Polycythemia?

Polycythemia is defined as an increase in red cell count, hemoglobin, and PCV. There are two main forms of polycythemia as absolute erythrocytosis and relative erythrocytosis; in absolute erythrocytosis, there is a true increase in the red cell volume and in relative erythrocytosis, there is a decrease in the plasma volume with a normal red cell volume.

Causes

Primary Polycythemia

• Polycythemia Vera
• Mutations in the erythropoietin receptor
• High oxygen affinity hemoglobins

Secondary Polycythemia

– Hypoxic increase in erythropoietin

• High altitude
• Chronic lung disease
• Heart disease
• Sleep apnea
• Morbid obesity
• Heavy smoking
• Increased affinity of hemoglobin

– Inappropriate increase in erythropoietin

• Renal cell carcinomas
• Hepatocellular carcinomas
• Adrenal tumors
• Cerebral hemangioblastomas
• Massive uterine leiomyoma
• Over administration of erythropoietin

The erythropoietin levels are normal or raised in secondary polycythemia.

Secondary polycythemias are treated through the management of the underlying cause. Any tumor that either directly or indirectly results in an increase in the erythropoietin production should be surgically resected. Heavy smokers are more likely to be affected by secondary polycythemia since the increased levels of carboxylated hemoglobin stimulate the natural pathways of erythropoietin production. Thrombosis, hemorrhage and cardiac failure are the complications of secondary polycythemia. Venesection can also be helpful in relieving the symptoms, especially if the PCV is more than 0.55/micro liter.

What is Polycythemia Vera?

Polycythemia vera is a clonal stem cell disorder in which there is an alteration in the pluripotent progenitor cell, leading to an excessive proliferation of erythroid, myeloid and megakaryocytic progenitor cells. A vast majority of the patients suffering from this condition have acquired mutations in the JAK2 gene.

Clinical Features

There is an insidious onset. The typical presentation is an elderly patient of more than 60 years of age complaining of tiredness, depression, vertigo, and tinnitus.

Other than these nonspecific symptoms, the patient can have,

• Hypertension
• Angina
• Intermittent claudication
• Bleeding tendency
• Severe itching after a good bath
• Gout
• Hemorrhages
• Thrombosis
• Plethora

Diagnostic Criteria

Major Criteria

• Hemoglobin level more than 185 g/l in men and 165 g/l in women
• The presence of JAK2 mutation

Minor Criteria

• Bone marrow biopsy showing hypercellularity for age with panmyelosis
• Decreased serum erythropoietin level
• Endogenous erythroid formation colony in vitro

At least one minor criterion with both the major criteria and one major criterion with any one of the minor criteria should be present to make a diagnosis of PV.

Management

The aim of the management is the maintenance of normal blood count to prevent complications such as thrombosis. The following interventions are the mainstays in the management of PV

• Venesection
• Chemotherapy
• Administration of low dose aspirin for the patients who have had thrombotic episodes previously.
• Administration of anagrelide to prevent megakaryocyte differentiation

30% of the patients with PV can have Myelofibrosis, and 5% of the patients can get myeloblastic leukemia.

What are the Similarities Between Polycythemia and Polycythemia Vera?

• Polycythemia vera is the most prominent cause of primary polycythemia.

What is the Difference Between Polycythemia and Polycythemia Vera?

Summary – Polycythemia vs Polycythemia Vera

Polycythemia is defined as an increase in red cell count, hemoglobin, and PCV. Polycythemia vera is a clonal stem cell disorder in which there is an alteration in the pluripotent progenitor cell leading to an excessive proliferation of erythroid, myeloid and megakaryocytic progenitor cells. Basically, there is no difference between Polycythemia and Polycythemia Vera. Polycythemia vera is one of the vast numbers of causes of polycythemia which is due to a defect in the JAK2 gene.

Reference:

1.Kumar, Parveen J., and Michael L. Clark. Kumar & Clark clinical medicine. Edinburgh: W.B. Saunders, 2009.

Image Courtesy:

1. “Red blood cells illustration”By Donald Bliss (Illustrator) – National Cancer Institute (Public Domain) via Commons Wikimedia
2. “US Navy 060505-N-2832L-050 Hospital Corpsman Megan Beach, checks the flow of blood through a cell saver, during training for an antilogous blood transfusion” By U.S. Navy photo by Journalist Seaman Apprentice Mike Leporati – (Public Domain) via Commons Wikimedia