Autoimmune thrombocytopenia in dogs and cats.

Autoimmune thrombocytopenia has been recognized as a distinct entity in the dog and cat. It is characterized by: (1) clinical signs of thrombocytopenia, such as hemorrhages into the skin and tissues and from body orifices, (2) coagulation defects related to thrombocytopenia, such as prolonged bleeding time and poor clot retraction, (3) hematologic changes such as severe to moderate thrombocytopenia, often blood loss anemia, and signs of increased erythropoiesis, and (4) an absence or decreased number of megakaryocytes in the bone marrow during early phase and increased number during compensatory phase. Megakaryocytes may also show morphologic abnormalities. Serologic diagnosis of AITP in the dog and cat currently involves demonstration of antiplatelet antibody in serum by PF-3 test and/or associated with marrow megakaryocytes by a technique of direct immunofluorescence. Circumstances leading to formation of antiplatelet antibody remain unknown. Immune-mediated platelet destruction is believed to occur in the reticuloendothelial system, primarily in the spleen. Treatment consists primarily of corticosteroids and other immunosuppressive drugs. Dogs with primary AITP generally respond favorably to such therapy.