Avaliação do status funcional da glândula tireoide comparado com parâmetros hematológicos, bioquímicos, histológicos e moleculares na pele de cães da raça Golden Retriever

Abstract

Canine hypothyroidism is overdiagnosed because it is a real challenge for clinicians. In addition to not presenting specific clinical signs, the diagnostic methods available in the clinical routine are flawed. Besides that, new studies have emerged evidencing that the usual reference values by species are exceeded and do not correspond to the real diagnostic. In order to evaluate the laboratory tests used to diagnose this endocrinopathy, 21 male Golden Retriever dogs, ranging from 4 to 12 years of age, were used. All animals showed some clinical signs suggesting hypothyroidism or laboratory-compatible signal, according to the literature. Futhermore, all dogs were evaluated for the daily intake of iodine due to the possibility that the hormonal results are compatible with the Wolff-Chaikoff effect. In the first phase of the study, free T4 (fT4) and thyroid stimulating hormone (TSH) were measured. Using the normal values for the species as reference, it was possible to distribute animals in two groups due to the statistical difference of T4ld (p = 0.023): (1) Euthyroid (n = 13) and (2) Hypothyroid (n = 8). It is important to note that there was no significant difference between the groups regarding the plasma TSH concentration (p = 0.0455). Clinically, there was no relationship between the signs presented with the hormonal results. Regarding iodine intake, it was possible to observe that all the animals were being submitted to diets with excess microelement, although these concentrations could not be related to the hormonal variation. Thereafter, the second phase of the study was started with 12 dogs submitted to the stimulation test with human recombinant TSH (rhTSH) and skin biopsy for histopathology and real-time PCR. This was used to determine the expression of type 2 deiodinase (D2) and type β thyroid hormone receptor (Trβ). The rhTSH stimulation test revealed a significant difference between total T4 concentrations before and after TSH in both groups (group 1: p <0.05, group 2: p <0.001). However, there was no statistical difference between those groups. Histopathological examination were inconsistent both to elicit the disease and to exclude it, suggesting that it is a faulty auxiliary examination. Nevertheless, when evaluating the hormonal results against the racial reference, it can be observed that in fact, there were 21 normotireoideos dogs and, therefore, the statistically insignificant results would be expected. In this way, it is possible to conclude that reference values should be used with caution and it is necessary to decrease the variables to improve the accuracy of the diagnosis