Aspectos anatomopatológicos da tireoide de gatos domésticos necropsiados na região central do Rio Grande do Sul (2022-2023)

Abstract

The thyroid is of great importance in feline medicine due to the high prevalence of hyperthyroidism in this species. This is considered the main endocrinopathy in elderly cats, being associated with primary follicular proliferative changes. Meanwhile, hypothyroidism is a rare endocrinopathy in felines. To date, there are few studies evaluating thyroid lesions in cats. The objective of this work is to characterize proliferative and non-proliferative thyroid changes in a population of 61 cats submitted to necropsy without prior clinical suspicion of thyroid changes. Our objective was also to investigate possible associations between the presence of proliferative thyroid lesions, affected age group and concomitant cardiac and renal lesions. To this end, collection and anatomopathological evaluation of the thyroids of cats submitted to necropsy (2022-2023) were carried out in a veterinary pathology laboratory in the central region of Rio Grande do Sul, Brazil. During necropsy, both thyroids were macroscopically analyzed, collected, fixed in 10% buffered formalin, routinely processed and stained using the hematoxylin and eosin (HE) technique. Of the 61 thyroids analyzed, 15 (24.6%) had some macroscopic change and 48 (78.7%) had some histological change, of which 33 had proliferative changes and 48 had some non-proliferative change. In the first manuscript, proliferative changes were analyzed. The proliferative lesions observed were hyperplasia (18/33 [54.5%]) and cystic adenoma (6/33 [18.2%]) and microfollicular carcinoma (1/33 [3.03%]). A positive correlation was observed between higher proliferative scores and older age. Approximately half (48.4%) of cats with a proliferative lesion had a proliferation score equal to or above A4, a score most frequently associated with hyperthyroidism. Of the 33 cats with proliferative thyroid lesions, 10 (30.3%) had hypertrophic cardiomyopathy and 11 (33.3%) had concomitant renal lesions. The results observed in this first study suggest that feline hyperthyroidism may be clinically underdiagnosed in this region. In the second manuscript, non-proliferative thyroid changes were investigated. Follicular cysts (28/61 [45,9%]), lipofuscin accumulation (28/61 [45,9%]) and ectopic thymic tissue (7/61 [11,5%]) were the most common findings, being the latter observed in young cats. Some of the non-proliferative lesions observed in this second study have the potential to cause hypo- or hyperthyroidism in felines. The high prevalence of histological changes in the thyroid of cats without prior clinical suspicion of thyroid disease in the central region of Rio Grande do Sul is the main finding of these two studies and highlights the importance of investigating thyroid changes in domestic cats, even in those individuals who do not present a palpable increase in thyroid volume. It is hoped that this study will contribute to increased research and improved diagnosis of hyper and hypothyroidism in cats.