Canine Idiopathic Thrombocytopenia (CIT)

Canine idiopathic thrombocytopenia (CIT) or Immune mediated thrombocytopenia (ITP), is an autoimmune disease. The body's immune system task is to fight foreign substances in the body, like germs and viruses. But in autoimmune diseases, the immune system attacks healthy tissues, not germs. In case of CIT, the bone marrow produces defective blood cells which are unable to control the blood clotting function.

Canine idiopathic thrombocytopenia (CIT), or Immune mediated thrombocytopenia (ITP) is a condition resulting from the immune system disorder when there are not enough platelets. Platelets are blood cells produced in the bone marrow that help blood to clot. These cells are involved in the initial phase of wound repair. This condition is sometimes associated with abnormal bleeding under the skin or from gums. It is more common in female dogs.

Thrombocytopenia may be congenital or acquired. Congenital thrombocytopenia may be caused by bone marrow malformations. It can also result as a consequence of transfer of maternal antibodies to the newborn. This is a rare condition.

Causes of Canine Idiopathic Thrombocytopenia

Numerous conditions may cause acquired thrombocytopenia including whole-body irradiation; drugs (levamisole, sulfonamide, antibiotics); toxins; viral, rickettsial or protozoan infections; chronic hepatitis; myelogenous leukemia; tumors (hemangiosarcoma); Addison's 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 commonly results from overly-active macrophage system or immune-mediated mechanisms. Immune-mediated thrombocytopenia (ITP) is one of the most common causes of thrombocytopenia in dogs where the dog's immune system produces antibodies which attack and destroy the blood cells.

Hereditary disorders causing thrombocytopenia are the Wiskott-Aldrich syndrome, a severe immunodeficiency disease characterized eczema.

The most common infectious cause of thrombocytopenia in dogs is ehrlichiosis Infection with Ehrlichia canis and, less commonly, with E. platysand E. ewingii cause thrombocytopenia. Other infections causing thrombocytopenia include infectious canine hepatitis virus, distemper vaccination, peritonitis, dapsone therapy, myasthenia gravis, immune-mediated hemolytic anemia (IMHA) (the ITP and IMHA may occur simultaneously).

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.

Thrombocytopenia in animals is also often associated with 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.

Females and small breeds of dogs, such as Cocker Spaniels, appear predisposed to immune-mediated thrombocytopenia, and the cause of this condition remains unknown. Most affected dogs are middle-aged females or spayed females.

Signs of Canine Idiopathic Thrombocytopenia

In mild cases, the affected dog may present with many pinpoint, purplish-red spots in the mucous membranes. These spots, known as petechiae, may develop into larger bruises in the mucous membranes and in the skin. These conditions occur due to internal bleeding. In addition, the dog may show signs of lethargy, weakness, and nosebleeds. Dogs that are more severely affected may show signs of blood in the urine and feces (making the color of the feces darker than usual).

Diagnosis of Canine Idiopathic Thrombocytopenia

The diagnosis of ITP is difficult, and is usually made by excluding other causes of thrombocytopenia.

Treatment of Canine Idiopathic Thrombocytopenia

The treatment of ITP involves using corticosteroids alone or in combination with other immunosuppressive drugs. Most dogs recover with single or multiple courses of treatment.

References:
1. Veterinary Hematology and Clinical Chemistry By Mary Anna Thrall
2. Essentials of Veterinary Hematology By Nemi Chand Jain
3. Hematology By Susan M. Cotter