Overcoming the diagnostic and therapeutic challenges of canine immune-mediated thrombocytopenia - Veterinary Medicine
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Overcoming the diagnostic and therapeutic challenges of canine immune-mediated thrombocytopenia
Determining that the immune system is the cause of a dog's decreased platelet count can be difficult. These clinicians walk you through the diagnostic and treatment process so you can help patients with this life-threatening bleeding disorder.


Additional diagnostic testing

Table 2. Causes of Canine Thrombocytopenia
Achieving a definitive diagnosis of immune-mediated thrombocytopenia can be challenging, because no single test is diagnostic.6 The diagnosis is primarily one of exclusion, thus, other causes of thrombocytopenia should be ruled out (Table 2).2,8

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 thrombocytopenia 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. < 30,000/μl). Thus, this test is not indicated in patients with marked thrombocytopenia.

Imaging. Evaluate for underlying neoplasia by performing thoracic and abdominal radiography and abdominal ultrasonography.8 Obtain fine-needle aspirates of enlarged organs, such as the liver, lymph nodes, and spleen, for cytologic examination if the platelet count is adequate (> 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 Immune-mediated 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


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