Planar thyroid scinti-graphy of a normal cat. The most commonly recognized signs of hyperthyroidism are weight loss, hyperactivity, and an increased appetite. An increased water consumption and urination are other common signs of feline hyperthyroidism that are thought to result from an increased blood flow to the kidneys.
Gastrointestinal signs are common in hyperthyroidism.
Intermittent vomiting and diarrhea are frequently noted. Cardiovascular signs including an increased heart rate, arrhythmias and congestive heart failure, are common in cats with hyperthyroidism. In these cats, the typical signs of hyperactivity and increased appetite are replaced by depression and inappetance. Weight loss may progress at an enhanced rate in these cats. In addition to these nonspecific signs, a majority of hyperthyroid cats will have an enlarged thyroid gland.