No statistically significant association between recent vaccination and a diagnosis of presumptive primary immune-mediated thrombocytopenia (IMT) was found in a recent retrospective study that examined 48 dogs presumed to have IMT and 96 control dogs.1
If vaccination is deemed necessary, vaccine administration can be staggered throughout the year. Medications or supplements the patient was receiving just before or during the first episode of IMT also should be avoided (when possible) in all future treatment protocols in that patient. All of these precautions may apply to other known immune-mediated conditions as well.
Although a statistically significant relationship between vaccination and IMT was not found in this study, the authors note that one cannot rule out the possibility of an infrequent association between the two or a transient, nonclinical, postvaccination IMT.1 They discuss several important limitations of the study, including a lack of information regarding the number of vaccines in the subject's lifetime, an inherent difficulty of confirming the diagnosis of idiopathic IMT, a small sample size and the study's retrospective nature. So it is difficult to conclude whether recent or cumulative vaccinations may or may not increase the risk of idiopathic IMT.
Because of the limited availability and variable sensitivity and specificity of antiplatelet antibody testing, IMT is typically diagnosed based on clinical and laboratory criteria, exclusion of other disease processes and response to treatment. IMT usually results in a severe thrombocytopenia (< 50,000/μl).
Signs of IMT
Patients with IMT typically present with petechiae (pinpoint hemorrhage), ecchymosis (bruising) or overt hemorrhage (e.g., epistaxis, gingival and intestinal bleeding, prolonged bleeding after injury). Patients may appear clinically normal, or they may be presented as emergencies because of anemia or as a result of bleeding into hollow cavities (e.g., hemothorax, hemoabdomen).
Consider these diagnostic tests if you suspect a patient has IMT: an accurate platelet count, a coagulation profile (e.g., activated clotting time, prothrombin time, partial thromboplastin time), a buccal mucosal bleeding time (to help rule out a platelet function disorder) and a von Willebrand antigen test.
In the case of secondary thrombocytopenia, the ideal treatment is to control or eliminate the underlying cause. However, in cases of idiopathic IMT, one or more immunosuppressants are typically used. In some patients with idiopathic IMT, an initial intravenous dose of vincristine or vinblastine may be given. Corticosteroids—specifically prednisolone—are the backbone of immunosuppressive therapy but are associated with a wide range of side effects.
If immunosuppression fails to control the IMT, consider splenectomy. Some case reports in the human literature have also described the use of oral melatonin in cases of refractory IMT.3
Dr. Lyman is a graduate of The Ohio State University College of Veterinary Medicine. He completed a formal internship at the Animal Medical Center in New York City. Lyman is a co-author of chapters in the 2000 editions of Kirk's Current Veterinary Therapy XIII and Quick Reference to Veterinary Medicine.
Dr. Runde is a graduate of the University of Pennsylvania School of Veterinary Medicine. He completed an internship at Hollywood Animal Hospital. He is an associate veterinarian at the Animal Emergency and Referral Center in Ft. Pierce, Fla.
1. Huang AA, Moore GE, Scott-Moncrieff JC. Idiopathic immune-mediated thrombocytopenia and recent vaccination in dogs. J Vet Intern Med 2012;26(1):142-148.
2. Boothe DM. Small animal clinical pharmacology and therapeutics. 2nd ed. St. Louis, Mo: Elsevier Saunders, 2012.
3. Todisco M, Rossi N. Melatonin for refractory idiopathic thrombocytopenic purpura: a report of 3 cases. Am J Ther 2002;9(6):524-526.