Goals of Treating Polycythemia
Polycythemia, also known as erythrocytosis, is an abnormal increase in the number or concentration of circulating red blood cells (RBCs). The symptoms and treatment of polycythemia vary greatly depending upon the underlying cause of the condition. It is important to determine which form of polycythemia is involved, so that an appropriate treatment protocol can be implemented. Most forms of polycythemia are treatable, and the sooner the treatments are started, the better. Secondary absolute polycythemia tends to be the most difficult (although not impossible) to treat. A veterinarian is in the best position to assess a dog’s condition and recommend the best treatment approach. The therapeutic goals are to restore the appropriate solid-to-fluid ratio in the affected dog’s blood and to relieve the symptoms of the disorder.
Relative polycythemia can usually be resolved by rehydration. The veterinarian can easily increase a dog’s blood fluid level by well-monitored intravenous or subcutaneous fluid therapy. Keeping the animal as calm as possible facilitates the rehydration process. The dog’s kidney function, electrolyte balance and other factors are important to the selection of the appropriate fluid or fluid combinations. Once the dog’s plasma level returns to normal, the relative polycythemia condition should be resolved. Transient polycythemia caused by splenic contraction normally is not clinically significant and does not require treatment.
Primary absolute polycythemia is an uncommon, chronic disease of domestic dogs that involves increased production and circulation of mature red blood cells due to abnormal proliferation of certain red blood cell precursors in bone marrow. The goal of treating primary absolute polycythemia is to reduce the viscosity (thickness) of the blood by reducing the circulating red blood cell mass and increasing the fluid component of blood (plasma). This is accomplished through a process called phlebotomy - a procedure where a defined amount of blood is permanently removed through a catheter inserted into a central vein. To prevent a dramatic drop in blood pressure, most veterinarians simultaneously administer isotonic fluids through a different intravenous catheter, in order to restore normal blood volume. A phlebotomy is sometimes referred to as “bleeding the animal.” It may take several of these procedures to correct polycythemia, and they may need to be repeated from time to time. If the underlying condition is quite severe, a medication called hydroxyurea, and/or chemotherapy medications such as chlorambucil or busulfan, can be administered to suppress red blood cell production by bone marrow. Owners should always discuss all treatment options with their veterinary professionals.
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 the one involved with primary absolute polycythemia. In order to treat secondary absolute polycythemia, the underlying cause of the condition must first be diagnosed. Once the cause is identified and treated (or at least controlled), polycythemia should be well-managed, if not eliminated entirely. In some cases, especially if the dog’s symptoms are severe, periodic therapeutic phlebotomies may be required.
The prognosis for most dogs with polycythemia is usually quite good, as long as appropriate therapy is implemented.