Fifteen dogs with immune mediated thrornbocytopenia (IMT) were studied retrospectively. All dogs had a thrombocyte count below 50,00O/pI when response to therapy was studied. Platelet counts greater than SO,OOO/pI were present in all dogs within 2-9 days of initiating medical therapy. Eight dogs experienced a single episode of thrombocytopenia and seven dogs relapsed over the following 5 to 24 months. Clinical parameters from dogs that experienced a single episode of IMT were compared with data from dogs that relapsed to determine whether any information would identify dogs that were prone to relapse. Signalment, severity of thrombocytopenia, and time to achieve a platelet count above 50,00O/pI were found not to differ (P > 0.05) between these two groups.Five of the seven dogs with relapsing I M T were splenectomized after 2 to 4 episodes (mean, 2.8 k 0.8) of thrombocytopenia over 2 to 14 months. The postoperative progress of these five dogs was followed for 6 to 17 months. Platelet counts were sustained above 200,00O/pI in 4/5 after splenectomy and it was possible to discontinue medical therapy in these dogs. In comparison, the 2 relapsing I M T cases that were not splenectomized continued to require intermittent immunosuppressive therapy.We conclude that signalment and routine pretreatment laboratory test results are not useful in distinguishing dogs with relapsing IMT from those that will experience one episode of IMT. Seemingly, splenectomy is useful in the management of dogs with relapsing IMT. (Journal of Veterinary Internal Medicine 1990; 4:4-7)

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