Introduction
Polycythemia, a condition in which the number or concentration of red blood cells in the bloodstream is actually or relatively elevated, can contribute to a number of different clinical signs depending upon why the condition occurred in the first place. There are several different types of polycythemia, and treatment decisions will be designed 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 changed usually due to dehydration, loss of plasma or blood or sudden contraction of the spleen. In other words, while the overall red blood cell mass remains normal, the fluid component has lessened for some reason, making the blood “thicker”, or more viscous. This type of polycythemia can cause nonspecific clinical signs of lethargy, difficulty breathing, fatigue, exercise intolerance, small red spots on the skin, shaking, seizures, vision difficulty, and possibly a blue tint to the skin. Dehydration and fluid loss can result from severe vomiting, diarrhea, decreased water intake and other reasons. Blood loss can happen for many reasons as well, both externally such as from a wound, to internal bleeding from trauma, parasites or otherwise. Extreme fear or excitement may cause the dog’s spleen to contract, releasing a burst of red blood cells into circulation. If you suspect that your dog has experienced any of these conditions or signs, an immediate trip to the veterinarian is warranted.
Absolute Polycythemia
Absolute polycythemia in dogs can be either primary or secondary. The primary form results from abnormal proliferation of red blood cell precursors in the bone marrow, causing too many blood cells to be made and sent into circulation. The clinical signs of this condition in dogs can include increased thirst, increased water intake and increased urination. Owners also may notice that mucous membranes are redder than normal, or red spots on the dog’s skin caused by the rupture of small capillaries. Changes in behavior can also be seen, including neurological signs of changed motor skills/coordination.
Secondary Absolute Polycythemia
Secondary absolute polycythemia results from abnormal increase in the kidneys’ production of a hormone called erythropoietin and 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 dogs, 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 or factors. Like primary polycythemia, signs of secondary absolute polycythemia may include a lack of interest in play or social interactions, seizures, confusion, lethargy, fatigue and difficulty walking, and other nonspecific signs.
If your dog experiences any of these symptoms, get to the veterinarian. Some forms of polycythemia are treatable, and the sooner the treatments are started the better. Secondary absolute polycythemia tends to be most difficult (although not impossible) to treat. Your veterinarian is in the best position to assess your pet’s condition, its causes and its best treatment approach.