The clinical syndrome known as hyperthyroidism is caused when functional thyroid tumors secrete excess thyroid hormone into the Beagle’s blood. The clinical signs of hyperthyroidism include weight loss, an increase in thirst and urination, an increase in appetite, aggressive behavior and hyperactivity. The thyroid tumors responsible for causing hyperthyroidism may be either small benign masses or, more often the case, malignant tumors. These malignant tumors are usually large solid masses that often will extend into the Beagle’s esophagus and trachea and into his surrounding musculature, thyroidal blood vessels and nerves. Commonly the tumor spreads (or metastases) to the lungs and lymph nodes as well.
The development of thyroid tumors, whether benign or malignant, usually averages around age ten, with a range of five to fifteen years. Any dog breed can be affected by thyroid tumors, but those who may have an increased risk are: Beagles, Boxers, German Shepherds and Golden Retrievers. The sex of the dog plays no part in risk.
Diagnosis of hyperthyroidism will require the documentation of increased circulating levels of thyroid hormone and the histologic (an microscopic examination of tissue) evaluation of a biopsy specimen obtained from the mass. Surgery is usually used to treat both benign tumors and small malignant tumors that have not yet spread. The prognosis for the Beagle following surgical removal is good. Treatment for large malignant masses that have spread extensively into surrounding tissue or to other areas of the body may involve a combination of surgery, radioactive iodine, chemotherapy and radiation therapy. For these types of tumors however, the Beagle’s prognosis is poor.