First off, let’s not confuse hyperthyroidism with hypothyroidism
Hyperthyroidism is an overactive thyroid where hypothyroidism is an underactive thyroid. Both conditions can be life threatening to your cat if not diagnosed and treated properly.
Commonality in Cats
Hyperthyroidism is a common disease in cats, and mostly afflicts cats middle-aged and older.
It’s caused by an increase in production of thyroid hormones (known as T3 and T4) from an enlarged thyroid gland in a cat’s neck. In most cases, enlargement of thyroid glands is caused by a non-cancerous tumor called an adenoma. Some rare cases of hyperthyroid disease are caused by malignant tumors known as thyroid adenocarcinomas.
Cats afflicted with hyperthyroidism usually develop a variety of signs that may be subtle at first but that become more severe as the disease progresses. The most common clinical signs of hyperthyroidism are weight loss, increased appetite, and increased thirst and urination. Hyperthyroidism may also cause vomiting, diarrhea, and hyperactivity. The coat of affected cats may appear unkempt, matted, or greasy.
A veterinarian who suspects a cat has a thyroid problem will conduct a physical examination and palpate the cat’s neck area to check for an enlarged thyroid gland. The cat’s heart rate and blood pressure may also be checked. If thyroid disease is a possibility, your veterinarian will likely order a blood chemistry panel and an analysis of thyroid hormone levels. Most cats with hyperthyroidism have elevated levels of the thyroid hormone T4 in their bloodstream, but a small percentage of cats with hyperthyroidism have T4 levels within the normal range.
There are four treatment options for feline hyperthyroidism: medication, radioactive iodine therapy, surgery, and dietary therapy. Each treatment option has its advantages and disadvantages. The treatment a cat receives for hyperthyroidism will depend on specific circumstances, including the patient’s overall health status, the owner’s ability and willingness to medicate the cat regularly, and financial considerations.
Antithyroid drugs act by reducing the production and release of thyroid hormone from the thyroid gland. These medications do not provide a cure for the disease, but they do allow either short-term or long-term control of hyperthyroidism. The advantages of medication are that the drugs are readily available and relatively inexpensive. Some cats may experience side effects from medication, including vomiting, anorexia, fever, anemia, and lethargy. Lifelong treatment, usually involving twice-daily oral dosage, will be required, and for some owners and cats, this dosage schedule may be difficult to maintain.
Radioactive Iodine Therapy
When available, radioactive iodine therapy is the treatment of choice for cats with hyperthyroidism. The advantages of radioactive iodine therapy are that the procedure most often cures hyperthyroidism, has no serious side effects, and does not require anesthesia. It does, however, involve the handling and injection of a radioactive substance that is only permitted at facilities specially licensed to use radioisotopes. The radioactivity carries no significant risk for the cat, but precautionary protective measures are required for people who come into close contact with the cat.
Removal of the thyroid glands, called surgical thyroidectomy, is a relatively straightforward surgical procedure that has a good success rate. The advantage of surgery is that it is likely to produce a long-term or permanent cure in most cats, and therefore eliminates the need for long-term medication. This surgery requires general anesthesia, however, and there might be added risks if older cats have heart, kidney, or other problems that could cause complications. One major risk associated with surgical thyroidectomy is inadvertent damage to the parathyroid glands, which lie close to or within the thyroid gland and are crucial in maintaining stable blood calcium levels.
Certain studies suggest that in some hyperthyroid cats, limiting the amount of iodine in the diet may be a viable option for treating this disease. This may be particularly useful in cats with medical conditions that make other treatment options impossible. Dietary restriction of iodine is, however, somewhat controversial because of concerns about the effects of long-term iodine restriction on overall health and the possibility that such a diet may actually backfire and worsen hyperthyroidism. Research into this potential treatment option is ongoing. Discuss these issues with your veterinarian when considering dietary iodine restriction as a treatment for hyperthyroidism in cats.
The prognosis for cats with hyperthyroidism is generally good with appropriate therapy. In some cases, complications involving other organs may worsen this prognosis. If you cat has hyperthyroidism or hypothyroidism, contact your vet to to learn more about what you can do.