Weight Loss

• One of the most common signs of canine hyperthyroidism is weight loss. Hyperthyroidism increases the dog's metabolism, causing him to lose weight.
  
  

Heart Rate

• Dogs with hyperthyroidism can also have an elevated heart rate, which can become a serious issue if left untreated.
  
  

Appetite

• Due to the elevated metabolism caused by hyperthyroidism, many dogs with the disorder will display an increase in appetite.
  
  

Changes in Behavior

• Hyperthyroidism causes the thyroid hormones T3 and T4 to be produced in excessive amounts. These elevated hormone levels can alter the behavior of an affected dog. Dogs with hyperthyroidism may show signs of hyperactivity, nervousness and increased water consumption and urination.
  
  

Treatment

• Thyroid cancer is the most common cause of hyperthyroidism in dogs. Surgery is necessary to remove tumors, along with chemotherapy and medications such as methimazole (Tapazole) to control hyperthyroidism.