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Immune-mediated thrombocytopenia in dogs | VETgirl Veterinary Continuing Education Videos

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In this VETgirl online veterinary continuing education video, we discuss immune-mediated thrombocytopenia (ITP) – otherwise called idiopathic thrombocytopenic purpura (ITP) – in dogs. In this video, we review etiology, clinical signs, treatment, and overall prognosis for this rare but potentially deadly immune-mediated disease in dogs in veterinary medicine.

This is a 7-year-old, male neutered, Lhasa Apso, who presented to the emergency service for lethargy, decreased appetite, and bruising. Upon examination, this dog was found to have petechiae and ecchymoses. In this dog, no platelets were found on a blood smear. This dog’s coagulation profile was normal (remember, PT/PTT are never affected by platelet count, unlike ACT and BMBT). The patient was positive for Lyme disease based on a 4Dx snap test.

First, a quick review of immune-mediated thrombocytopenia. ITP may be due to either primary (idiopathic) or secondary causes, with primary being the most frequent form in dogs. Secondary causes include tick-borne infections, paraneoplastic causes (e.g., lymphoma, etc.), drug reactions (e.g., estrogens, sulfonamides and chloramphenicol), chemotherapy, and bone marrow neoplasia. In patients with ITP, antiplatelet antibodies coat platelets, resulting is a shorter platelet lifespan and increased destruction. ITP most commonly occurs in middle-aged, female dogs, and certain breeds (e.g., Cocker Spaniels, Poodles, Old English sheepdogs, etc.) are overrepresented. Clinical signs of ITP are due to severe thrombocytopenia (typically < 25-50,000 platelets). Spontaneous bruising in the form of petechiae, ecchymoses, scleral hemorrhage, epistaxis, melena, joint swelling, hyphema, hematuria, etc. may be seen. Large cavital bleeds (e.g., hemoabdomen, hemothorax, pericardial effusion) are less common with ITP, as this is more associated with factor deficiencies (e.g., anticoagulant rodenticide poisoning, etc.). Normally, canine patients should have between 200,000 to 500,000 platelets, each with a lifespan of about 8 days. Dogs with ITP typically have < 50,000 platelets. With ITP, each platelet has a significantly reduced life span as well as decreased efficacy, resulting in spontaneous bruising and bleeding.

Treatment for this dog included fluid therapy, immunomodulation, and prevention of complications. First, the patient should be treated with fluid therapy for the hypoperfused state (if clinical signs of hemorrhage are significant). Next, immunomodulation with steroids and cyclosporine remain the primary medications used today. Depending on patient response, vincristine, azathioprine, cyclophosphamide, or even IVIG may be required. Prevention of complications may include the use of low-dose aspirin (to prevent a hypercoagulable state), GI protectants, and transfusions if needed. While most transfusion products are not beneficial, they can be useful for anemia (from blood loss). Also, fresh whole blood (which has not been refrigerated) can be used in cases of severe, life-threatening bleeds. Platelet-rich plasma can be considered, along with lyophilized platelets; however, this is not readily available.

When treating patients with ITP, gentle handling is imperative due to the risk of bleeding. Care should include minimal venipuncture, and no jugular sticks, cystocentesis procedures, or neck leads. While the prognosis is generally guarded to fair, aggressive treatment and supportive care may yield a favorable prognosis, with up to 84% of dogs reported to survive to time of discharge. However, long term immunomodulation is warranted and owners should be counseled on the long term side effects (e.g., PU/PD, polyphagia, muscle wasting, increased risk of thromboembolic disease, etc.).

References:
1. O’Marra SK, de Laforcade AM, Shaw SP. Treatment and predictors of outcome in dogs with immune-mediated thrombocytopenia. J Am Vet Med Assoc 2011;238(3):346-52.

2.Bianco D, Armstrong PJ, Washabau RJ. A prospective, randomized, double-blinded, placebo-controlled
study of human intravenous immunoglobulin for the acute management of presumptive primary
immune-mediated thrombocytopenia in dogs. J Vet Int Med 2009;23(5):1071-1078.

3.Bianco D, Armstrong PJ, Washabau RJ. Treatment of severe immune-mediated thrombocytopenia with human IV immunoglobulin in 5 dogs. J Vet Int Med 2007;21(4):694-699.

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