Introduction | Causes & Prevention | Symptoms & Signs | Diagnosis & Test | Treatment Options

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Introduction

Polycythemia is a condition involving an increase in the relative or absolute number or concentration of circulating red blood cells (RBCs). Polycythemia is also called erythrocytosis (another name for red blood cells are "erythrocytes"). The signs and treatment of polycythemia vary greatly depending on the cause of the condition. There are two general types of polycythemia in cats: relative and absolute. It is important to determine which type is involved in a given animal, so treatment can be tailored accurately.

How Polycythemia Affects Cats

Polycythemia can cause a number of vague clinical signs, which can appear abruptly or over time. These include lethargy, difficulty breathing, anorexia, fatigue, exercise intolerance, nose bleeds (epistaxis), stunted growth, development of small red spots on the skin, shaking, seizures, vision difficulties and either brick red or sometimes pale mucous membranes. Owners often notice increased thirst, increased water intake and increased urination. Owners also may notice that their sneeze excessively. Changes in behavior can also be seen, including neurological signs of altered motor skills, confusion and incoordination.

Causes & Prevention

Causes of Polycythemia in Cats

Relative polycythemia, sometimes called spurious polycythemia, is an apparent or relative elevation in circulating RBC numbers normally due to dehydration, blood loss, shock or splenic contraction. In cases of relative polycythemia, no extra red blood cells are actually made by the cat's body. The condition results from changes in the relative levels of the liquid and solid components of blood. For example, vomiting and diarrhea can cause dehydration by depleting the overall amount of fluid in the cat's body, resulting in relative polycythemia. Blood loss can occur for many reasons as well, either externally from a wound or internally from trauma, parasites, surgical hemorrhage or otherwise. Transient polycythemia is a type of relative polycythemia that can occur when a cat experiences extreme excitement, fear or shock. This can cause the spleen to contract, releasing a large number of red blood cells from storage into circulation and elevating the relative ratio of cells to fluid in the blood.
Absolute polycythemia results from increased bone marrow production of RBCs and may be either primary or secondary. The cause of primary absolute polycythemia is unknown, but it occurs as an inherited defect in cattle and is uncommon in cats and in dogs. This is a chronic condition that leads to overgrowth of red blood cell precursors in the bone marrow, which in turn causes overproduction of new, normal RBCs. Basically, the blood becomes too thick, because the cellular/more solid components are elevated while the fluid component remains relatively normal.
Secondary absolute polycythemia is caused by an abnormal increase in the kidneys' production of erythropoietin (EPO), a renal hormone that stimulates red blood cell production when there is an inadequate oxygen supply to bodily tissues (called "hypoxia"). Availability of oxygen supply to the body can be insufficient for many reasons, such as adaptation to high altitude, various forms of cancer, renal cysts or other forms of renal disease, hyperthyroidism, heart or lung disease or other causes of circulatory insufficiency. Regardless of cause, secondary absolute polycythemia is the result.

Preventing Polycythemia

There is no way to reliably prevent polycythemia. Obviously, preventing dehydration and blood loss will help prevent relative polycythemia. Primary absolute polycythemia cannot be prevented as veterinary medical experts do not yet understand its cause. Secondary absolute polycythemia is only preventable if the underlying cause of hypoxia can be prevented or managed.

Special Notes

Most cats with polycythemia can be successfully managed for many years.

Symptoms & Signs

Polycythemia, a condition in which the number or concentration of red blood cells in the cat's bloodstream is actually or relatively elevated, can contribute to a number of different clinical signs depending upon why the condition developed in the first place. There are several different types of polycythemia, and treatment decisions should be based upon the underlying cause.

Clinical Signs of Polycythemia

Relative Polycythemia

Relative polycythemia occurs when the ratio of red blood cells-to-fluid in blood is increased, usually due to dehydration, loss of plasma or loss of whole blood. In other words, while the overall red blood cell mass remains normal, the fluid component becomes decreased for some reason, making the blood "thicker," or more viscous. This form of polycythemia can cause a number of nonspecific clinical signs, including lethargy, difficulty breathing, fatigue, exercise intolerance, small red spots on the skin, shaking, seizures, vision difficulty and sometimes a pale blue-ish tint to the skin. Another form of polycythemia, called transient polycythemia, can produce these same symptoms but is caused by contraction of the spleen, which injects red blood cells into circulation. This is normally not a medical problem in companion animals and tends to occur with exercise or excitement.

Absolute Polycythemia

Absolute polycythemia in cats can be either primary or secondary. The primary form results from abnormal proliferation of red blood cell precursors in the bone marrow, basically causing too many red blood cells to be made and sent into circulation. The clinical signs of this condition can include lethargy, anorexia, nose bleeds (epistaxis), seizures, stunted growth, increased thirst, increased water intake and increased urination. Owners also may notice that their cats' mucous membranes are brick red, and they may sneeze excessively. Changes in behavior can also be seen, including neurological signs of altered motor skills and coordination.

Secondary absolute polycythemia is caused by an abnormal increase in the kidneys' production of a hormone called "erythropoietin" - also known as "EPO." EPO stimulates red blood cell production through a mechanism that is different from the bone marrow disease causing primary absolute polycythemia in cats, and often is activated by inadequate oxygen distribution to body tissues (called "hypoxia"). Secondary absolute polycythemia can be caused by heart disease, kidney or liver disease, attempts to adjust to high altitude, various forms of cancer, renal cysts and other conditions. Like primary absolute polycythemia, signs of secondary absolute polycythemia may include a lack of interest in play or social interactions, lethargy, seizures, confusion, incoordination, fatigue, motor impairment and other nonspecific signs.

If your cat experiences any of these symptoms, visit your veterinarian as soon as you can. Some forms of polycythemia are treatable, and the sooner treatment begins the better your cat's chances of recovery. Secondary absolute polycythemia tends to be most difficult (although not necessarily impossible) to treat. Your veterinarian is in the best position to assess your cat's condition and determine the best treatment approach.

Treatment Options

Polycythemia is an abnormal increase in the number or concentration of circulating red blood cells ("RBCs"). Polycythemia is also known as erythrocytosis (another name for red blood cells are "erythrocytes"). The signs and treatment of polycythemia vary greatly depending on the cause of the condition. There are two main types of polycythemia in cats, relative and absolute. These can further be broken down into primary and secondary absolute polycythemia. It is important to determine which type is involved in a given animal so that treatment can be tailored appropriately.

Treating Polycythemia

Relative Polycythemia

Relative polycythemia is typically treated by inpatient rehydration using intravenous or subcutaneous fluids, the selection of which depends upon the functional status of the cat's kidneys and other organ systems. A veterinarian can easily increase a cat's overall body fluid levels by well-monitored fluid therapy. Keeping the cat as calm as possible can facilitate the rehydration process. Once the animal's fluids levels return to normal, the condition should be resolved.

Absolute Polycythemia - Primary

Primary absolute polycythemia is the result of an uncommon but chronic bone marrow disorder in cats. The cause is not well understood. Basically, the blood becomes too thick, because the solid components are elevated while the fluid components remain relatively normal. Initial treatment of absolute primary polycythemia is to reduce the viscosity of the blood by reducing the number of circulating RBCs. This is accomplished through therapeutic phlebotomy – a procedure where a predetermined amount of blood is removed from one of the cat's central veins. To prevent the patient's blood pressure from dropping dramatically because of rapid blood loss, veterinarians usually simultaneously administer a roughly equivalent volume of saline through a different catheter. Phlebotomies sometimes are called "bleeding the animal" and may need to be repeated periodically. If the underlying condition is severe, certain medications can be administered to suppress red blood cell production by the bone marrow. Discuss the consequences of these treatments with your veterinary professional.

Absolute Polycythemia – Secondary

Secondary absolute polycythemia occurs when the kidneys produce too much erythropoietin ("EPO"), a hormone that regulates red blood cell production through a different mechanism than that causing primary absolute polycythemia. Normally, the kidneys in cats make and release EPO in response to hypoxia, which is an insufficient availability of oxygen to body tissues. A number of conditions can cause inadequate oxygen supply, such as adaptation to high altitude, insufficient production of EPO by the kidneys due to cancer, cysts or other forms of renal disease, hyperthyroidism, hyperadrenocorticism, heart or lung disease or other causes of circulatory insufficiency. Regardless of cause, secondary absolute polycythemia is the result. In order to treat secondary absolute polycythemia, the cause of the condition first must be diagnosed and controlled. In some cases, especially if the cat's signs of polycythemia are severe, periodic therapeutic phlebotomies also will be recommended.

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