Hyperthyroidism in Two Dogs With a Functional Thyroid Gland Carcinoma

Introduction and Case Report:

Thyroid cancer should be one of the top list differentials for a neck mass in older, large-breed dogs, as they make up 1 to 4% of the cancer cases reported [3, 5, 7]. Carcinomas and adenocarcinomas represented 90% of thyroid cancers and though the majority of carcinomas are unilateral and nonfunctional, 10 to 25 % of them may be functional [1 - 5]. No sex predisposition appears to be evident, but studies show that dogs between 10 and 15 years of age have a significantly increased chance of developing thyroid disease [5].

The overwhelming majority of thyroid cancers are carcinomas and they are most common in Golden Retrievers, Beagles, and Siberian Huskies [4, 5]. Thyroid carcinomas are often rapidly growing, with invasion of adjacent tissues, such as the trachea, larynx, esophagus, and jugular vein [6]. Unilateral tumors are about twice as frequent as bilateral, and a palpable cervical enlargement is the predominant clinical abnormality observed in most cases [6, 8]. Never the less, when the tumour is functional, sings of hyperthyroidism may be present, even before a neck mass is palpable.

Studies reveal that the median survival time (MST) for dogs with mobile thyroid carcinomas treated with surgery alone is greater than 36 months with survival rates of 75% and 70% for 1and 2years, respectively. Otherside, the MST for dogs with fixed thyroid carcinomas treated wiith surgery alone is only of 7-10months with 1- and 2-years survival rates of 25% and 10%, respectively [4,9].

A 13-year-old 21.9-kg neutered male Podengo and a 4-year old 24,5-kg fertile male Siberian Husky were presented to the Hospital Veterinário da Bicuda with history of dermatological problems, polyuria and polydypsia, polyphagia, weight loss, decrease in appetite, gastrointestinal disorders, syncope and hind limb weakness. Physical examination revealed the presence of a palpable oval mass on the ventral surface of the neck caudal to the cricoid cartilage of the larynx, mobile on the 13-year old dog and fixed on the 4-year old dog. In the 13-year old dog were also detected a grade V/VI left apical systolic heart murmur and grade IV/VI right apical systolic heart murmur, with sinus tachycardia.  […]