RESUMEN
OBJECTIVE: Characterization of clinical and clinicopathological parameters as well as the treatment and course of the disease in dogs with suspected primary immune-mediated thrombocytopenia (pIMT), and identification of characteristics in comparison to secondary IMT (sIMT). MATERIAL AND METHODS: Medical records of thrombocytopenic dogs with a positive platelet-bound-antibody (PBA)-test performed between 2003 and 2008 were evaluated retrospectively. Dogs were suspected of having pIMT by exclusion of other diseases potentially associated with sIMT, and sIMT was diagnosed when an associated disease could be detected. Dogs with an incomplete follow-up were excluded from the study. RESULTS: Thirteen of 21 dogs (62%) suspected of having pIMT were male. Median age of the affected dogs was 6.6 years (1.6-13.5 years [MINIMUM-maximum]). Spontaneous bleeding was observed in 18 dogs (86%) mainly in the form of surface bleeding. Nineteen dogs (91%) with pIMT had platelet counts below 20,000/µl. All dogs with pIMT, for which platelet volume analysis was available, displayed a mean platelet volume (MPV) within or below the reference range. Fourteen of 15 dogs in which bone marrow analysis was performed had an increased megakaryopoiesis. Comparison of two different treatment regimes (prednisolone versus prednisolone and azathioprine) did not result in a significantly different platelet count recovery time. There was no significant difference regarding age and sex distribution between dogs with pIMT and sIMT. Platelet count and MPV were significantly lower in dogs with pIMT than in dogs with sIMT. Increased megakaryopoiesis was more frequently detected in dogs with pIMT compared to dogs with sIMT. CONCLUSION AND CLINICAL RELEVANCE: Dogs with a positive PBA-test and additionally a severe thrombocytopenia, low MPV and activated megakaryopoiesis are likely to have pIMT.