Thyroid lesions in a population of domestic cats submitted to necropsy without clinical suspicion of thyroid disease

Although hyperthyroidism is the most common endocrine disorder in elderly cats, systematic studies investigating the prevalence of thyroid lesions in feline animals are scarce. Our objective was to evaluate morphological changes in the thyroid glands of 61 cats submitted to necropsy without clinical suspicion of hyperthyroidism. Thirteen (13/61 [21.3%]) cats had thyroid enlargement and 54/61 (88.5%) had some histological thyroid changes. Proliferative lesions were histologically seen in 33/61 (54%) cats while non-proliferative lesions were observed in 48/61 (78.7%) cats. Thyroid hyperplasia (18/33 [54.5%]) and cystic adenoma (6/33 [18.2%]) were the most prevalent proliferative changes and lesions with little or no clinical significance (37/61 [60.6%]), degenerative (31/61 [50.8%]) and inflammatory changes (12/61 [19.7%]) were the most common non-proliferative changes. Among cats with proliferative lesions, 16/33 (48.4%) had a proliferation grade ≥A4, a grade previously associated with clinical hyperthyroidism. Although the cats from this study did not have any clinical diagnosis of thyroid disease, it is possible that one or more had some degree of clinically unnoticed thyroid dysfunction. The high prevalence of follicular lesions in this study highlights the importance of a more careful clinical and pathological investigation regarding thyroid diseases in mature and elderly cats.