Veterinary Medicine - August 2007 - (Page 532)

Immune-mediated thrombocytopenia O P E E R - R E V I E W E D Blood testing and urinalysis. In addition to a CBC, perform a serum chemistry profile and urinalysis (collected by free catch) as part of a minimum database. 8,13 Consider heartworm testing. 8 Perform serum antibody titers to rule out rickettsial and fungal disorders based on the geographical location and travel history. Anaplasma platys (formerly Ehrlichia platys) causes a severe cyclic thrombocytopenia in dogs, but the dogs are usually asymptomatic.6 Measure prothrombin time, an activated partial thromboplastin time, and fibrin degradation products or D dimer concentrations to determine whether the throm- bocytopenia is accompanied by other hemostatic abnormalities.6 Clinical pathology abnormalities that suggest a consumptive coagulopathy (disseminated intravascular coagulation) include schistocytes, prolonged coagulation times, elevated fibrin degradation products or D-dimer concentrations, and decreased fibrinogen concentrations, particularly in patients with concurrent clinical illness.2,8 Activated clotting time can be falsely prolonged if the platelet count is < 10,000/µl.1,6 A buccal mucosal bleeding time assesses primary hemostasis and will be prolonged in patients with very low platelet counts (e.g. 50,000/µl); otherwise, such sampling is unsafe.6 Bone marrow aspiration. If concurrent leukopenia (with or without anemia) is not present, bone marrow aspiration is not needed for most patients.2 Bone marrow aspiration may be indicated if an underlying cause is not apparent after thorough clinical evaluation and if inadequate bone marrow platelet production is suspected because large, immature platelets are absent.1,4 Thrombocytopenia is not a contraindication for bone marrow aspiration or biopsy; although bruising may occur, severe hemorrhage is uncommon.1,2,6 The proximal humerus is often selected as the aspiration site because muscle mass can be avoided and pressure can be applied to achieve hemostasis after the procedure. With immune-mediated thrombocytopenia, the bone marrow is characterized by increased total megakaryocyte numbers, as the marrow tries to respond by increasing platelet production.1 This bone marrow response should occur within three to five days of an acute thrombocytopenic episode.6 Immunemediated megakaryocyte aplasia is rare in dogs.2 Definitive diagnosis. A clinical diagnosis of immune-mediated thrombocytopenia is usually based on finding a moderate to severe thrombocytopenia; seeing no evidence of additional hemostatic abnormalities or nonimmunologic platelet sequestration, consumption, or destruction; and finding macrothrombocytosis or microthrombocytosis.2,6,8 Causes of Canine Thrombocytopenia Decreased production of platelets by the bone marrow • Drugs—estrogens, phenylbutazone, sulfonamides, chloramphenicol, dapsone, myelosuppressive chemotherapy • Irradiation • Infectious disorders—chronic ehrlichiosis • Neoplasia—myelodysplasia or myeloproliferative disorder, myelophthisis, estrogen-secreting tumor • Myelofibrosis • Antibody-mediated megakaryocyte damage Sequestration of platelets in vascular spaces • Splenic disease—splenic torsion, splenic neoplasia • Vascular tumor—hemangioma or hemangiosarcoma Decreased circulating platelet life span via platelet consumption • Disseminated intravascular coagulation • Hemangiosarcoma • Hemolytic uremic syndrome (rare) • Vasculitis Decreased circulating platelet life span via platelet destruction • Immune-mediated thrombocytopenia —Primary —Secondary—Other autoimmune disorders (systemic lupus erythematosus, rheumatoid arthritis, immune-mediated hemolytic anemia), drugs (gold salts, trimethoprim-sulfonamide), vaccines, neoplasms, infections (viral, bacterial, rickettsial, protozoal, parasitic), or after incompatible transfusion • Nonimmunologic —Disseminated intravascular coagulation —Microangiopathy —Infection (ehrlichiosis) Acute severe blood loss 532 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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.