Veterinary Medicine - August 2007 - (Page 529)

cause of thrombocytopenia may be multifactorial. Neoplasia may cause thrombocytopenia through immune-mediated and non-immune-mediated mechanisms. Non-immune-mediated mechanisms include platelet consumption, splenic sequestration, hemorrhage, myelophthisis, and bone marrow suppression by chemotherapy or radiation.2,8 Hemolytic uremic syndrome, a rare cause of thrombocytopenia, is readily differentiated based on renal failure, microangiopathic hemolytic anemia, and fever.2 Decreases in platelet number resulting from splenic sequestration are generally modest.2 Similarly, thrombocytopenia resulting from blood loss is generally mild and transient, although moderate to severe thrombocytopenia has been reported with anticoagulant rodenticide intoxication.8,11 Immune-mediated thrombocytopenia usually causes severe thrombocytopenia—often < 50,000 platelets/µl.1 A severe, inherited thrombocytopenia has been reported to occur in up to 50% of Cavalier King Charles spaniels.12 Platelet counts can be as low as 20,000/µl, but many affected dogs have macrothrombocytes, and this disorder is not associated with a bleeding tendency. Perform manual platelet counts in dogs of this breed with thrombocytopenia, as large platelets may result in falsely low platelet counts as measured by impedance analyzers. Bone marrow disorders can cause thrombocytopenia, but if thrombocytopenia is the sole abnormality on a complete blood count (CBC), bone marrow disorders are unlikely. With the exception of early estrogen toxicity, bone marrow disorders that cause thrombocytopenia typically cause concurrent leukopenia, with or without anemia.1,2 The presence of a marked, nonregenerative anemia or neutropenia could suggest bone marrow disease; alternatively these findings may be seen with immune-mediated disease. DIAGNOSTIC APPROACH Signalment Middle-aged dogs are most commonly affected by immune-mediated thrombocytopenia, but the disease can occur in dogs of any age. A high prevalence has been reported in miniature, toy, and standard poodles; cocker spaniels; Old English sheepdogs; and German shepherds, but any breed, including crossbreeds, may be affected.1,2,6 The high prevalence in some breeds may suggest a genetic predisposition. Although dogs of either sex may develop immunemediated thrombocytopenia, about twice as many female dogs are affected compared with male dogs.1,2 Clinical presentation Dogs with immune-mediated thrombocytopenia are often not presented for evaluation of bleeding, but rather for nonspecific clinical signs such as lethargy, weakness, or anorexia. 1,2,6 Some affected dogs are asymptomatic. In these dogs, a low platelet count on a CBC may be the first indication of immune-mediated thrombocytopenia. Dogs with secondary immune-mediated thrombocytopenia could present for evaluation of clinical signs related to the underlying disease (e.g. peripheral lymphadenopathy with lymphoma or dyspnea with disseminated histoplasmosis). 6 Other dogs with immune-mediated thrombocytopenia have signs of hemorrhage with a history of otherwise being apparently healthy.1 Unexpected hemorrhaging after trauma or routine surgery, is also a manifestation of immune-mediated thrombocytopenia.1,7 Bleeding related to immune-mediated thrombocytopenia is typical of that expected with primary hemostatic disorders (Table 1). Bleeding from mucous membranes may cause gingival, nasal, conjunctival, preputial, penile, or vaginal hemorrhage.1,6 Petechiae or ecchymotic hemorrhages on the mucous membranes and skin, especially on the ventral abdomen, are typical (Figure VETERINARY MEDICINE August 2007 529 http://virbacvet.com http://virbacvet.com

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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