Cintilografia de tireoide e radioiodoterapia com dose individualizada em gatos com doenças tireoidianas

Abstract

Nuclear imaging exams are generally limited to academic institutions and scientific research. In Brazil, veterinary scintigraphy for dogs and cats was not commercially available until 2022, limiting the evolution of Brazilian nuclear medicine. The availability of the service in 2022 made it possible to evaluate the thyroid scans and diseases of dogs and cats in a larger number of animals. Thyroid scintigraphy is a simple and non-invasive procedure that provides information about the morphology and function of glandular tissue essential in the diagnosis and treatment of thyroid diseases. This work was divided into four parts. The objective of the first part was to carry out a literature review on feline hyperthyroidism, thyroid scintigraphy, radioiodine therapy and thyroid tumors in cats. The following three parts were written in scientific article format and had the following objectives: (1) report a series of cases of six cats with hyperthyroidism submitted to radioiodine therapy with the new individualized dose algorithm after the scintigraphy study; (2) characterize 123 feline thyroid scintigraphy exams using two different collimators (LEHR and Pin-hole); and (3) report a series of seven cases of felines diagnosed with hyperthyroidism and SHIM-RAD tumors and treated with a high dose of Iodine-131 (I131) in nuclear veterinary medicine centers in Spain and Brazil. In the first article, the radioiodine therapy protocol using individualized doses based on scintigraphy findings, hormonal dosage and iodine uptake by thyroid tissue, proposed by Peterson and Rishniw (2021), was used with some changes. Euthyroidism was achieved in all six cats reported in an evaluation carried out twelve months after treatment. The feline scintigraphy images were conclusive for the diagnosis of hyperthyroidism and essential for the treatment protocol. The algorithm for calculating individual doses of I131 was successfully reproduced in this case series report. In the second article, the evaluation of 123 feline scintigraphy studies highlighted some rare findings and described clinical cases little reported in the veterinary medical literature, such as the scintigraphy characteristics of pleural effusion, SHIM-RAD tumors diagnosed in three animals, congenital hypothyroidism in father and son, iatrogenic hypothyroidism in a feline treated with potassium iodide and two cases of hypothyroidism due to dyshormoniogenesis in adult felines. The study also demonstrated the importance of obtaining images using the Pin- hole collimator to better define thyroid morphology and characterize glandular disease and, in addition, suggested that the heterogeneous pattern of radiopharmaceutical distribution in the glandular parenchyma is associated with cystic thyroid disease. In the third article, the seven animals diagnosed with SHIM-RAD tumors were treated with high doses of I131. In these animals, the association between patient's history, clinical manifestations, scintigraphy findings and the final diagnosis of SHIM-RAD tumor was fundamental for the clinical approach and therapeutic planning of the seven animals described, and the animals presented an excellent response to the therapy using doses above 15mCi of I131.