Hyperthyroidism - Excess Thyroid Hormone in Cats

4 min read



Outpatient management is usually sufficient if drugs that inhibit the production of thyroid hormones can be used. Surgical removal of the thyroid gland, or treatment using a radioactive form of iodine will require inpatient treatment and monitoring.


Surgical removal of the thyroid gland is best performed when only one thyroid gland is affected, as removal of both can possibly lead to hypothyroidism. Another complication that can occur after surgical removal of the affected thyroid gland is the successive hyper-activity of the remaining thyroid gland.


The use of radioiodine is restricted to a confined medical facility, since the treatment itself is radioactive. Depending on the state in which you live and the guidelines in place, your cat will need to be hospitalized from several days to a few weeks after being treated with radioactive medicine, to allow the radioactive material to clear most of the body before the cat is handled by family members. Precautions will still need to be taken after taking your cat home, to reduce your risk of having a toxic reaction to the radioactive treatment. Your veterinarian will advise you in precautionary measures.


Anti-thyroid drugs can also be effective. However, drugs to control thyroid activity often must be give for the life of the cat. In rare cases, untreated hyperthyroidism can lead to congestive heart failure, which requires emergency, inpatient intensive care. Poor absorption of nutrients and high metabolism in untreated hyperthyroidism suggest the need for a high protein, highly digestible diet; that is, one that can be quickly absorbed into the body.


Once the major symptoms resulting from excessive levels of thyroid hormones in the body have been resolved, dietary modifications often do not need to be strictly enforced. Even so, dietary modifications may be necessary to treat or control complications such as kidney damage.


Living and Management


Once treatment has begun, your veterinarian will need to reexamine your cat every two to three weeks for the initial three months of treatment, with a complete blood count to check for serum thyroid hormone concentration of T4. The dosage of the medications will be adjusted to maintain T4 concentration in the low-normal range.


If your cat has had surgery, particularly removal of the thyroid gland, your veterinarian will want to closely observe the cat's physical recovery. Development of low blood-calcium levels and/or paralysis of the voice box during the initial postoperative period are complications that will need to be watched for and treated, should they occur. Your doctor will also be measuring thyroid hormone levels in the first week after surgery and every three to six months thereafter, to check for recurrence of thyroid gland over activity. 


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