Hyperthyroidism in Cats

Hyperthyroidism is a disease of older cats, caused by excessive production of thyroid hormones. The usual cause for increased hormone production is a tumor of the thyroid gland. These tumors may be benign (non-cancerous), or malignant. The reason these glands develop tumors is not yet known.

Signs of excessive thyroid production include weight loss despite a ravenous appetite, frequent bowel movements, increased thirst and urination, restlessness, hyperactivity, frequent crying or vocalizing, neglect of normal grooming, a rapid heart beat, abnormal heart rhythm, or a heart murmur. The effects on the heart may be severe and result in congestive heart failure. Other symptoms can include vomiting or diarrhea.

In most cats, a blood test measuring the thyroid hormone level, may be all that's needed to diagnose the condition. In some cats, with a normal level, but who clinically appear hyperthyroid, further more complicated testing may be indicated to confirm the condition.

To properly stage the disease, your cat should get a complete examination, including different blood tests, and x-rays. This is to ensure an overall healthy pet, to diagnose other concurrent illnesses ( a lot of hyperthyroid cat also have kidney disease), and to be sure that the tumor-if present-has not already spread to the chest or other internal organs.

Three major therapies are available to your cat if diagnosed with hyperthyroidism:

1. Medical management: This is accomplished through treatment with an anti-thyroid drug such as methimazole (Tapazole® ). The side effects this drug can have are as follows: poor appetite, vomiting, scratching at the face and neck, liver toxicities, bone marrow suppression resulting in low platelet or white cell counts, or anemia.
2. Surgery: This involves anesthesia and removal of the offending gland. This can be difficult in an older animal, especially if other medical problems are present that make anesthesia even more risky. However, once the surgery is completed, and as long as the tumor doesn't recur or occur on the other side, the condition is cured.
3. Radioactive Iodine treatment: This procedure must be done in a radioactive safe facility, usually a referral hospital. Radioactive iodine , in a quantity safe to the body is administered to the patient. The thyroid, whose role it is to regulate iodine metabolism, "gathers" the radioactive iodine. The amount of radiation now concentrated in the thyroid, is enough to kill off the cancerous tissue. No anesthesia or surgery or potentially harmful drugs are necessary. The major drawback of this procedure is its cost.