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Hyperthyroidism in Cats 1

While uncommon in dogs, hyperthyroidism is often seen in cats. The average age of a cat diagnosed with hyperthyroidism is 13 years, although the disease has occurred in cats from 4 to 22 years old. The disease does not seem to appear more often in one sex or any particular breed of cat. Hyperthyroidism occurs when the cat produces an excessive amount of thyroid hormone. Some of the symptoms of hyperthyroidism are gradual in onset and may no be noticed by the owner of the cat for months. The condition caused by over-production of the thyroid hormone is called thyrotoxicosis and it causes an overall increase in the metabolic rate of the cat’s tissues. The pet owner often notices that the cat has a ravenous appetite, yet is losing weight. Often, strange behavior, for example, the cat has consumed a whole loaf of bread or paces around the table while the family is eating a meal, will be noticed by the owner.

Weight loss occurs in approximately 90 percent of cats with hyperthyroidism. Other common signs of the disease include excessive urination (polyuria) probably accompanied by excessive thirst (polydipsia). The cat suffering from hyperthyroidism may have an unkempt haircoat and even patchy areas of complete hair loss. The cat may be extremely hyperactive or irritable and may vomit often and have diarrhea. Less commonly reported signs may include weakness, depressed activity, tremors, panting or labored breathing and increased volume of feces. It should also be noted that a very small percentage of cats suffering from hyperthyroidism actually stop eating.

Feline hyperthyroidism may be treated by administration of an antithyroid drug, radioactive iodine, or by surgical removal of the thyroid gland. Drug therapy controls – but does not cure – the disease. Therefore, if you veterinarian recommends drug therapy as treatment for your cat suffering from hyperthyroidism, that treatment must be continued for the life of the pet. Radioactive iodine treatment and surgical removal of the thyroid gland are both curative measures. Each of these treatment options has advantages and disadvantages for the patient and owner, and your veterinarian can provide you with explanations of each options.

A medication called methimazole is the drug therapy usually used in the long-term control of feline hyperthyroidism and for stabilization of thyroid hormone levels in cats prior to treatment with radioactive iodine or surgery. Methimazole is available in tablet form, however, some cats are not easy to “pill”, and an oral suspension can be prepared by compounding pharmacists for those patients. There is a possibility of side-effects in some animals, however, through careful monitoring by the veterinarian, pet owner and pharmacist, adjustment to the dosage usually relieves any problems