HEALTH

"THROMBOCYTOPENIA"

Thrombocytopenia refers to an abnormally low blood-concentration of platelets, which are blood cells that promote blood clotting after injury to the lining of the blood vessels. When the concentration of platelets becomes too low, bruising and bleeding may occur. Dogs with blood platelet concentrations of less than 40,000 per microliter of blood are at risk for spontaneous bleeding.

Abnormally low platelet numbers in blood can be caused by a variety of disease processes. These include failure to produce new platelets in the bone marrow, premature destruction of circulating platelets often by the body's own immune system, sequestration or storing of platelets in organs, and consumption of platelets at a rate that exceeds production in the bone marrow.

Dogs of either gender, any age and any breed can suffer from thrombocytopenia.

The severity of bleeding associated with thrombocytopenia depends on how low the platelet numbers fall.

In general, the lower the platelet count, the more likely bleeding is to occur.

What to Watch For
 
  • Small red spots on the white parts of the eyes (sclera), the gums or the skin
  • Bruises on the skin (ecchymoses)
  • Nose bleeds (epistaxis)
  • Bloody urine
  • Bloody stool

    • Diagnosis

    Tests are needed to recognize thrombocytopenia and exclude other diseases. Tests may include:
     
  • A complete medical history and physical examination. Your veterinarian will ask about previous vacinations and drug administration as possible factors in the development of thrombocytopenia.
  • A complete blood count (CBC or hemogram) including a platelet count to identify thrombocytopenia and anemia that may arise from bleeding
  • Serum biochemistry tests to evaluate for abnormalities in other organ systems and to evaluate the general health
  • Urinalysis to evaluate for infection, bleeding (hematuria) or protein loss that may occur as a complicating problem in some causes of thrombocytopenia
  • X-rays of the chest or abdomen to evaluate for the presence of other diseases such as infections or cancer that may be associated with thrombocytopenia.
  • Specific tests for infectious diseases like tick-borne diseases such as Rocky Mountain Spotted Fever or ehrlichiosis.
  • Bone marrow aspiration to obtain a sample for laboratory analysis if there is concern that your dog's bone marrow may not be making adequate numbers of platelets or may have been invaded by cancer.    This procedure often is performed under sedation with a local anaesthetic to numb the biopsy site.
  • Other tests of blood clotting. Body-wide abnormalities in coagulation (disseminated intravascular coagulation) can result in massive consumption of platelets.
  • Immune system function tests if an immune-mediated disease is suspected. In this case the body fails to recognize the platelets as part of itself and attacks them as if they were foreign invaders. The body may consider the platelets as foreign invaders if they become coated with certain drugs or infectious agents.

    Treatment

    Treatment for thrombocytopenia depends on the underlying cause of the low platelet count.
     
  • Unless your dog is bleeding, only the underlying cause of the thrombocytopenia is be treated. If a specific cause can be treated successfully, the blood platelet concentration soon returns to normal.
  • Corticosteroids (cortisone-like drugs) are often used to stop the immune system from destroying platelets.
  • Antibiotics, especially tetracyclines, often are prescribed until specialized test results for infectious diseases are available. Tetracycylines are chosen because they are effective against bacterial agents called rickettsia that may cause thrombocytopenia, as in ehrlichiosis and Rocky Mountain spotted fever.

  • It is difficult to increase platelet numbers adequately by transfusion, and transfused platelets do not last very long – a few days at most. Transfusion of whole blood, which contains plasma and all blood cell types including red blood cells and platelets, or packed red cells, which contains red blood cells without plasma, may be necessary in the event of life-threatening hemorrhage or if your dog is anemic from previous blood loss. Platelet-rich plasma is difficult to prepare and is not widely available for dogs.

    Home Care and Prevention

    Administer as directed all medications prescribed by your vet. Keep your dog calm and confined indoors to prevent bleeding and bruising. Watch for signs of bleeding or bruising and call your veterinarian immediately if such signs occur or worsen.

    Prevent tick bites whenever possible because ticks transmit the bacterial agents (rickettsia) that cause ehrlichiosis and Rocky Mountain spotted fever, diseases that cause thrombocytopenia. Use tick preventives and check your dog daily for ticks during warm weather. Other causes of thrombocytopenia are not preventable.

    • Thrombocytopenia does not always lead to excessive bleeding. Normally, there are more than 600,000 platelets per microliter of blood, which is about one millionth of a quart. Platelet numbers in blood must fall to about 10,000 to 40,000 per microliter before spontaneous bleeding becomes likely. Moderate thrombocytopenia may be found in animals with no evidence of bleeding and this finding often serves as a clue to an important underlying disease process.
    Thrombocytopathia is a term that refers to abnormal function of platelets. Animals with thrombocytopathia have adequate numbers of platelets in their blood, but the platelets do not function properly. Thrombocytopathia may be inherited or acquired. Acquired defects in platelet function may be due to drugs (such as aspirin), cancer or organ failure (such as kidney failure, liver failure).

    Coagulation refers to the clotting ability of blood, and normal coagulation arises from the combined effects of properly functioning platelets, blood vessel lining cells (endothelium) and protein clotting factors found in the blood and tissues. Deficiency or abnormal function of any of these components can cause spontaneous bleeding. Occasionally, a disease causes defects in more than one of these components simultaneously.

    The following disease processes may cause symptoms similar to those seen in dogs with severe thrombocytopenia:

     
  • Vasculitis. This inflammatory disease of blood vessels is characterized by tiny defects in the lining that can allow blood to leak from the vessels. Platelets are attracted to these defects and attempt to plug the holes. Consequently, vasculitis often also results in thrombocytopenia. Several different disease processes can cause vasculitis, including some types of infection and abnormal immune system function that results in an attack against the vessel walls
     
  • Von Willebrand's disease. The is an inherited defect in a body protein that normally facilitates the attachment of platelets to each other and to damaged vessel walls. Animals with this disorder have prolonged bleeding times and sometimes experience excessive bleeding after minor injury or surgical procedures. It is an inherited trait in several breeds of dogs, notably pinschers.
     
  • Insufficient quantities of coagulation proteins. Inherited deficiency of a coagulation protein is known as hemophilia. Certain disease processes such as liver failure can result in acquired deficiency of coagulation proteins.
     
  • Warfarin. Ingestion of this compound, a common ingredient in rat poisons, can result in a life-threatening bleeding disorder. Some of the currently available rat poisons contain ingredients that have the same effect as warfarin but are much more potent and longer acting. These poisons affect vitamin K metabolism such that coagulation proteins cannot be properly activated.
     
  • Disseminated intravascular coagulation (DIC). This refers to life-threatening bodywide coagulation that occurs as a complication of several serious diseases including infections and cancer. During development of DIC, tiny clots form throughout the body in small blood vessels. Both platelets and coagulation proteins are consumed in the formation of these small clots. Widespread life-threatening bleeding occurs when the body's platelets and coagulation proteins become depleted.
     
  • Disease in specific organs or body locations. Diseases can cause bleeding that is localized to those areas. For example, bladder stones can cause blood in the urine, nasal tumors can cause bleeding from the nostrils (often primarily on one side), gum disease can cause bleeding around the teeth, and trauma can cause bruising or bleeding.
     
  • Skin rashes can be mistaken for the tiny pinpoint hemorrhages called petechiae that are found in animals with severe thrombocytopenia. When finger pressure is placed on the red spots in a rash, the redness typically blanches out whereas with petechiae, the redness stays.

    • Diagnosis In-depth

    Specific diagnostic tests will be needed for your veterinarian to diagnose thrombocytopenia, determine its underlying cause and determine the effects of thrombocytopenia. Tests may include:

  • A complete medical history and physical examination. You should be prepared to provide a complete history about your dog. Important questions will be asked about your dog's home environment including time spent outdoors, travel history, previous illnesses, recent vaccinations or medications (e.g. aspirin, antibiotics) and any symptoms you have noticed. Factors such as your dog's age, breed and gender will influence the types of diseases your veterinarian will consider as possible causes of thrombocytopenia.

    Mild to moderate thrombocytopenia usually does not cause spontaneous bleeding and causes no abnormalities on physical examination. Severe thrombocytopenia, however, often causes characteristic abnormalities on physical examination.
     
  • These abnormal findings include tiny pinpoint hemorrhages on the gums, whites of the eyes (sclera) or skin called petechiae, and skin bruising called ecchymosis. Bleeding into body cavities or joints is not common in animals with thrombocytopenia. Your veterinarian also may examine the backs of your dog's eyes for evidence of bleeding with an instrument called an opthalmascope
     
  • A complete blood count (CBC or hemogram) including a blood platelet concentration to determine if your dog has thrombocytopenia and to evaluate for anemia that may have resulted from blood loss
     
  • Serum biochemistry tests to evaluate other organ systems and to determine the general health of your dog
     
  • Urinalysis to evaluate for blood in the urine (hematuria), infection, or protein in the urine that may occur with some diseases that cause thrombocytopenia

    Unfortunately, a highly reliable diagnostic test is not available for one of the most common causes of severe thrombocytopenia in dogs called immune-mediated thrombocytopenia or idiopathic thrombocytopenic purpura (ITP). Immune-mediated diseases result when the body's immune system fails to recognize its own cells and tissues and begins to attack them as if they were foreign invaders. In immune-mediated thrombocytopenia, the immune system attacks and destroys platelets. Due to lack of a reliable and specific diagnostic test for this disease, immune-mediated thrombocytopenia usually is diagnosed by ruling out other known causes of thrombocytopenia.

    Additional diagnostic tests may be recommended on a case-by-case basis to determine the cause of thrombocytopenia and to insure that your dog receives optimal medical care. Examples of additional tests may include the following:
     
  • Tests of the immune system. Systemic lupus erythematosus (SLE) is a generalized autoimmune disease that can cause damage to many tissues such as kidneys, joints, and skin and can result in destruction of platelets. The LE cell preparation and anti-nuclear antibody (ANA) test are two tests that may be requested if your veterinarian suspects your dog may have systemic lupus erythematosus. Immune-mediated destruction of platelets alone is more common than systemic lupus erythematosus.
     
  • Tests for specific infectious diseases. Results of the medical history, physical examination and other blood tests often determine whether or not specific tests for infectious diseases are necessary. Some infectious diseases that may be considered include tick-borne diseases such as Rocky Mountain spotted fever and ehrlichiosis. Other infectious diseases can cause blood platelet concentrations to decrease, but most of these other diseases cause only mild thrombocytopenia.
     
  • X-rays of the chest or abdomen to evaluate dogs with thrombocytopenia. Enlargement of the spleen often is observed in dogs with immune-mediated thrombocytopenia or infectious causes of thrombocytopenia since the spleen is a common site of platelet destruction. Enlargement of the spleen often can be identified on X-rays of the abdomen.
     
  • Abdominal ultrasound examination if your veterinarian suspects a tumor or enlargement of abdominal organs. After clipping the hair and applying a gel to facilitate transmission of ultrasound waves, a probe is held against the abdomen and ultrasound waves create images of the abdominal organs. This same technology is often used in pregnant women to visualize the fetus. If abdominal ultrasound is necessary, your veterinarian may refer your dog to a veterinary radiologist or internist for evaluation.
     
  • If a mass or enlarged organ is identified, a biopsy may be recommended to identify the nature of the mass or enlargement. A biopsy specimen may be obtained by surgery or using a specialized biopsy needle inserted through the body wall under ultrasound guidance.
     
  • If your veterinarian is concerned that your dog's bone marrow is not producing adequate numbers of platelets, a biopsy or needle aspirate of the bone marrow may be performed. This procedure is performed using a local anaesthetic to numb the biopsy site after the animal is sedated.
     
  • Other tests of clotting ability may be recommended. Common clotting function tests include prothrombin time and activated partial thromboplastin time, which evaluate two clotting pathways in the body.

    Specific treatment of dogs with thrombocytopenia depends on the cause. If the animal is not bleeding and the platelet count is not seriously low, the underlying cause of the thrombocytopenia is usually treated without specifically attempting to treat the thrombocytopenia itself. If the specific cause of thrombocytopenia can be treated successfully, platelet numbers will increase quickly. The best approach is to treat the underlying disease responsible. If thrombocytopenia is severe and likely to result in bleeding, the following may be considered:

  • Blood transfusion. It is difficult to increase the platelet count significantly with blood transfusion alone, and transfused platelets last only hours to days. Despite this, life-threatening bleeding may be treated with transfusion of whole blood, which contains all blood components including plasma and cells; packed red cells, which contain only red blood cells; or platelet-rich plasma, which contains only platelets and plasma.

    • If your dog is markedly anemic from blood loss, transfusion of whole blood or packed red blood cells may be necessary to provide red cells to carry oxygen to the tissues. Platelet-rich plasma is difficult to prepare and is not widely available in veterinary medicine.
     

  • Corticosteroids. Cortisone-like drugs such as prednisone often are used to inhibit destruction of the platelets by the immune system. Immune-mediated destruction of platelets is a common cause of severe thrombocytopenia, and corticosteroids often are used as soon as severe thrombocytopenia is identified.
     
  • Antibiotics, tetracyclines. These drugs are often used until results of specific tests for infectious disease are available. Many of the infectious agents that cause thrombocytopenia, such as the rickettsial agents that cause Rocky Mountain Spotted Fever and ehrlichiosis, are responsive to treatment with tetracycline.
     
  • Elimination of other drugs. If possible, any drugs your dog was receiving before developing thrombocytopenia will be discontinued because many drugs can cause thrombocytopenia.
     
  • Vincristine. This is a cancer chemotherapy drug that also can accelerate the release of platelets from the bone marrow where they are produced. If the bone marrow is functioning normally, vincristine may be administered to accelerate platelet release from the marrow.
     
  • Cyclophosphamide (Cytoxan) and Azathioprine (Imuran) are other drugs that may be used in dogs with suspected immune-mediated thrombocytopenia, especially those dogs that have not responded adequately to corticosteroids. These drugs have strong immunosuppressive effects and also can have potentially serious adverse effects. They should be used only with close veerinary supervision.
     
  • Splenectomy. Removal of the spleen may be recommended in dogs with immune-mediated thrombocytopenia that respond poorly to medical treatment. It may also be used in those cases in which sequestration of platelets is suspected, because the spleen is a major site of platelet destruction and sequestration. The spleen is submitted for microscopic examination by a veterinary pathologist after removal. The spleen should not be removed if the thrombocyotpenia is caused by an infectious agent.

    • Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be crucial. Administer as directed any medications prescribed by your vet and notify your vet if you are experiencing problems treating your dog.

    If your dog is at home while his platelet count is very low, keep the animal calm and confined to minimize the chance of bruising and bleeding. Observe your dog closely for signs of bleeding. Look at the whites of the eyes (sclera), gums, and skin for characteristic red spots (petechiae) or bruises (ecchymoses). Call your veterinarian immediately if you observe any petechiae, bruising, or bleeding or if your dog becomes very lethargic or shows any abnormal behavior.

    Return to your veterinarian on a regular basis to re-evaluate the platelet count until platelet numbers approach normal. There is no substitute for an accurate blood platelet count.

     


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    Updated 20-10-08

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