Canine Idiopathic Thrombocytopenia
Canine idiopathic thrombocytopenia (CIT), also called immune mediated thrombocytopenia (ITP), is a type of hematologic disease characterized by an abnormally low number of thrombocytes (platelets) resulting from the destruction of the blood cells by a dog's own immune system. Platelets are blood cells produced in the bone marrow that help blood to clot and are involved in the initial phase of wound repair. Thrombocytopenia may be congenital or acquired. The condition is sometimes associated with abnormal bleeding under the skin or from the gums. Females and small breeds of dogs appear predisposed to immune-mediated thrombocytopenia. Most affected dogs are middle-aged or spayed females.
Numerous factors are involved in the development of acquired thrombocytopenia. These include bone marrow malformations, transfer of maternal antibodies to the newborn, irradiation, and drugs. Drug sensitivity leading to thrombocytopenia may develop within a few days of initiation of drug therapy. Discontinuance of the offending drug is rapidly accompanied with return to the normal platelet levels. Other agents include toxins; viral, rickettsial and protozoan infections; chronic hepatitis; myelogenous leukemia; tumors (hemangiosarcoma); Addison disease; vitamin B12 or folate deficiencies; severe iron deficiency or immune-mediated disorders. Overdose of intravenous heparin may induce severe thrombocytopenia in cats. Increased platelet destruction may also result from overly-active macrophage and other immune-mediated mechanisms. The most common infectious cause of thrombocytopenia in dogs is ehrlichiosis, canine hepatitis virus, and distemper virus. In addition, thrombocytopenia has been associated with peritonitis, myasthenia gravis, immune-mediated hemolytic anemia. Thrombocytopenia is also often associated with disseminated intravascular coagulation (DIC), a disorder when the dog's blood clotting mechanisms are activated throughout the body instead of being localized to an area of injury. As a result, the blood clotting factors (proteins) are used up to such a degree that they not available to form clots at sites of real tissue injury. Severe bleeding, whether acute or chronic, is unlikely to cause thrombocytopenia because of the extra platelets stored in the spleen and other sites.
In mild cases, affected dog may present with signs of lethargy, weakness, and nosebleeds. There are multiple petechiae (pinpoint, purplish-red spots) in the mucous membranes and skin due to internal bleeding. Dogs that are more severely affected may show signs of blood in the urine and feces. The diagnosis of ITP is difficult. Treatment involves corticosteroids alone or in combination with other immunosuppressive drugs. Most dogs recover with single or multiple courses of treatment.
- Mary Anna Thrall. Veterinary Hematology and Clinical Chemistry
- Nemi Chand Jain. Essentials of Veterinary Hematology
- Susan M. Cotter. Hematology