Clinical Manifestation and Diagnosis of a Thyroid Adenoma in a 3-year-old Horse

Abstract

Hyperthyroidism in horses is a rare disorder in young horses that causes diverse findings such as weight loss, tachypnea, aggression, change in appetite and cachexia. In this report, the clinical manifestation and methods that used in the diagnosis of thyroid adenoma are presented. It was learned that a 3-year-old male Thoroughbred horse became aggressive and had been losing weight despite an adequate diet and appetite. During the inspection, a palpable, painless and moving mass was detected caudal to the larynx, on the left side. For further diagnosis, hemogram, serum biochemistry, urine dipstick analysis and ultrasonographic examination were performed. In serum biochemistry, high HDL, LDH, triglyceride, AST, direct bilirubin, creatine kinase and fT3; low TSH, fT4 and ferritin levels were determined. Ultrasonographic examination revealed that the left thyroid tissue was 2.83 cm x 4.81 cm in size. In the microscopic examination of the aspirate, it was observed that follicles were rich in cytoplasm and surrounded by cuboidal epithelial cells of varying sizes. Dilatation was observed in some follicles, while others were small or even atrophic. As a result, high fT3 and low TSH levels were consistent with the fact that the gland was overactive, the circulating thyroid hormone level was high, and the pineal gland produced less TSH by the feedback mechanism, all of which indicated hyperthyroidism. In addition, it was concluded that thyroid adenoma can also be seen in young horses, may cause clinical symptoms, ultrasonographic examination, microscopic examination of the aspirate and comprehensive serum biochemistry analysis are sufficient for diagnosis.