The diagnosis of feline hyperthyroidism is routinely made based on the measurement of elevated circulating levels of the thyroid hormones thyroxine (T 4) and triiodothyronine (T 3). The clinical signs usually reflect the stimulatory nature of thyroid hormones on the various organ systems. The multisystemic effects of hyperthyroidism result in signs that reflect dysfunction in many organ systems. The clinical signs of hyperthyroidism may vary from extremely mild (in some cases no clinical signs are recognizable) to severe. Clinical Signsįeline hyperthyroidism occurs in middle-aged to old cats with no breed or sex predilection.
In addition to these nonspecific signs, a majority of hyperthyroid cats will have an enlarged thyroid gland. Weight loss may progress at an enhanced rate in these cats. In these cats, the typical signs of hyperactivity and increased appetite are replaced by depression and inappetance.
Apathetic hyperthyroidism represents an unusual form of hyperthyroidism that occurs in approximately 10% of cats with hyperthyroidism. Most cats with hyperthyroidism develop a reversible form of heart disease with congestive heart failure developing in 10 to 15% of these cats. Cardiovascular signs including an increased heart rate, arrhythmias and congestive heart failure, are common in cats with hyperthyroidism. Intermittent vomiting and diarrhea are frequently noted. Gastrointestinal signs are common in hyperthyroidism. 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. The most commonly recognized signs of hyperthyroidism are weight loss, hyperactivity, and an increased appetite. The elevated circulating levels of the thyroid hormones thyroxine (T 4) and triiodothyronine (T 3) that occur in hyperthyroidism result in a multisystemic disease. Shortly thereafter it became recognized as the most common endocrine disorder of the cat. Feline hyperthyroidism was first described as a spontaneous disease in 1979.
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