2016 ACVIM Forum Research Abstract Program

Mean serum concentrations of T 4 and fT 4 were significantly higher and TSH was significantly lower during levothyroxine administration compared to baseline in both groups. Mean serum concentrations of T 4 , fT 4 and TSH beginning 1 week after levothyroxine was discontinued were significantly different compared to values during levothyroxine administration but not compared to baseline values. When groups 1 and 2 were compared, there was no difference in mean T 4 , fT 4 , and T 3 concentrations between groups during or after levothyroxine supplementation. Suppression of the HPTA occurred during levothyroxine supplementation, with mean serum T 4 , fT 4 and TSH concentrations returning to the reference interval by 1 week after discontinuation in both groups. It appears that assessing thyroid function tests 1 week after longterm levothyroxine supplementation may reliably establish dogs as being euthyroid. Autoantibodies directed against the P450 side chain cleavage enzyme (P450scc) have been recently described in a proportion of dogs affected with hypoadrenocorticism, consistent with an immune-mediated disease process. In humans affected with Addison's disease, autoantibodies can have a predictive value, being detected prior to clinical signs developing, and have been shown to persist post-diagnosis. Furthermore, an autoantibody positive status post-diagnosis has been associated with successful remission of Addison's disease following B-cell depletion with rituximab, suggesting active pathology in these cases.