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 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 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.