Veterinary Medicine - August 2007 - (Page 528)

Immune-mediated thrombocytopenia O P E E R - R E V I E W E D immune-mediated thrombocytopenia have been ruled out.6 TABLE 1 Secondary immune-mediated thrombocytopenia In secondary immune-mediated thrombocytopenia, antibodies bind to antigens adsorbed to the platelet surface or immune complexes nonspecifically bind to the platelet.5 Secondary immune-mediated thrombocytopenia occurs as a result of an underlying disorder.1,2 Many underlying causes of secondary immune-mediated thrombocytopenia have been reported. Often there is an association between a disease and thrombocytopenia, but the causative role has not been confirmed experimentally. 1 Conditions that have been associated with immune-mediated thrombocytopenia include autoimmune disorders, drug therapy, blood product transfusion, vaccine administration, various neoplasms, and infectious agents. Autoimmune diseases. Immunemediated thrombocytopenia may occur in association with other autoimmune diseases in dogs such as systemic lupus erythematosus, rheuma- Clinical Signs Typical of Primary and Secondary Hemostatic Disorders Primary hemostatic disorders Petechial and ecchymotic hemorrhages Bleeding from mucosal surfaces Immediate bleeding from venipuncture sites Secondary hemostatic disorders Hematoma formation Bleeding into body cavities (abdomen, thorax, joints) Delayed bleeding from venipuncture sites trimethoprim-sulfonamide combinations.1,2 Drugs generally act as haptens, which combine with platelets to form a drug-platelet complex that is antigenic.7 Drug-related immune-mediated thrombocytopenia usually develops weeks to months after initial therapy, resolves within two weeks of discontinuing therapy, and does not recur unless the drug is readministered.2,8 Severe thrombocytopenia caused by the production of antiplatelet antibodies has been reported in dogs within weeks after blood product transfusion.3 Vaccine administration. Canine postvaccinal immune-mediated thrombocytopenia has been suspected, but giosarcoma, nasal adenocarcinoma, and fibrosarcoma.1,9 Antibody against tumor antigens that are closely related to platelet membranes may initiate platelet destruction. In some dogs with solid neoplasms, thrombocytopenia resolves after tumor remission.1 Infectious agents. Viral, bacterial, rickettsial, protozoal, and parasitic infections may also play a role in inducing immune-mediated thrombocytopenia. 2 Infections may result in immune-mediated platelet destruction by exposing antigenic sites on platelet surfaces or through immunecomplex injury to platelet membranes.7 Antibodies that can bind to platelets have been identified in dogs with ehrlichiosis, babesiosis, leishmaniasis, and dirofilariasis. 2,7,10 The pathogenesis of thrombocytopenia with several infectious diseases is multifactorial, involving decreased production by the bone marrow and splenic sequestration, in addition to immune-mediated destruction.8 Drug-related immune-mediated thrombocytopenia usually resolves within two weeks after you discontinue the drug. toid arthritis, and immune-mediated hemolytic anemia.3 Drug and blood product therapy. Although any drug could provoke this disease, several drugs have been associated with immune-mediated thrombocytopenia in dogs, including auranofin (gold salts), cefazedone, and NON-IMMUNE-MEDIATED CAUSES When evaluating a patient with suspected immune-mediated thrombocytopenia, be sure to exclude nonimmune-mediated causes. Other mechanisms of thrombocytopenia include decreased platelet production due to bone marrow disorders, platelet sequestration, non-immunemediated platelet destruction, platelet consumption, and platelet loss. The evidence of a direct causative role of vaccines in immune-mediated thrombocytopenia is lacking.1 Neoplasia. Thrombocytopenia is commonly associated with various hematopoietic and solid neoplasms, including lymphoma, mammary adenocarcinoma, mast cell tumor, heman- 528 August 2007 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - August 2007

Contents A Veterinary Medicine Interview Veterinary Voices Idea Exchange Diagnosis and Treatment of Solar Dermatitis in Dogs Diagnostic Imaging for Linear Foreign Bodies in Cats Overcoming the Diagnostic and Therapeutic Challenges of Canine Immune-Mediated Thrombocytopenia Ophthalmic drugs: What’s new? CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - August 2007

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