Polycythemia

Polycythemia is a rare disorder of the bone marrow that causes the overproduction of all three blood cell lines: white blood cells, red blood cells, and platelets. The causes of this disorder are still investigated. There is some evidence that polycythemia results from primary pathologic processes such as cardiovascular disease or kidney problems, including tumors or bone marrow disease. The disease usually develops slowly, and most patients do not have clinical signs.

Types of Polycythemia

There are several types of polycythemia: primary, secondary adequate, and secondary inadequate polycythemia. Primary polycythemia can be a primary bone marrow disorder called polycythemia vera. Signs may include excessive thirst and urination, bleeding from small capillaries, and neurological disturbances due to increased density of blood. Secondary polycythemia is stimulated by lack of oxygen and may occur with primary cardiac or pulmonary disease or methemoglobinemia (e.g., acetaminophen intoxication in cats). Secondary polycythemia can also occur with kidney tumors.²

Signs

Patients with polycythemia vera also have an increased tendency to form blood clots that can result in strokes or heart attacks. Some can develop bluish skin discoloration, exercise intolerance, red skin spots, tremors, seizures, difficulty breathing, lethargy, and uveitis.¹ Puppies with this condition feed poorly and fail to thrive. Some dogs with polycythemia may exhibit canine compulsive disorder, a condition in which dogs display abnormal behavior.¹

Treatment

Treatment includes phlebotomy in which a vein is incised for the letting of the blood at 2-4 day intervals until packed cell volume (PCV) is normal. Phlebotomy may need to be repeated at 2-3 month intervals. Chemotherapy using chlorambucil may be effective.

Dogs with secondary inadequate polycythemia present with apathy, gait disturbances and disorientation, seizures (most probably because of formation of blood clots leading to low level of blood oxygen. Even after emergency treatment the general state deteriorates resulting in blood infections (sepsis). Dogs with secondary complications have a poor prognosis, and are euthanized.

References

1. Journal of Veterinary Behavior: Clinical Applications and Research Volume 1, Issue 1, July 2006, Pages 23-28
2. Ancillary Notes for Clinical Hematology (Washington State University, College of Veterinary Medicine)

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