Evaluation of thyroglobulin autoantibodies in dogs at the time of diagnosis of hypoadrenocorticism and during treatment.

BACKGROUND: Autoimmune thyroiditis (AIT) may occur more frequently in dogs with hypoadrenocorticism (HA) than previously recognised. The objective of this study was to determine the presence of thyroglobulin autoantibodies (TgAAs) in dogs with HA. METHODS: Dogs were included if HA was confirmed by an adrenocorticotropic hormone stimulation test conducted between 2019 and 2023. Serum total thyroxine, thyrotropin and TgAA were analysed from samples taken before and during HA treatment. RESULTS: Thirty-seven dogs were enrolled, with nine dogs showing positive TgAA titres at enrolment. Following HA treatment, TgAA became undetectable in six dogs; two showed persistent positive TgAA results and one was lost to follow-up. Additionally, two dogs that were initially TgAA negative developed hypothyroidism during the follow-up period. The overall prevalence of concurrent HA and hypothyroidism after initiation of hormone replacement therapy was three of 30 among the dogs for which follow-up data were available. LIMITATIONS: The retrospective nature of the study, small sample size and incomplete follow-up data for some patients limit the conclusions that can be drawn. CONCLUSION: Our findings demonstrate the concurrent occurrence of two different autoimmune diseases, AIT and HA, and show that the presence of TgAA can completely resolve with cortisol replacement therapy. Therefore, it is recommended to reassess thyroid function after initiating HA treatment to avoid unnecessary lifelong thyroxine supplementation.