Hyperthyroidism is the most common endocrine, or hormonal disorder of older cats. It is caused by excessive production of thyroid hormone which can lead to a wide variety of negative effects. The thyroid gland consists of two lobes which are located in the neck on either size of the trachea. Most cases are caused by hyperplasia (a non- cancerous enlargement) of one or both of the nodules. The enlarged nodule produces excessive amounts of the thyroid hormone. The thyroid hormone is normally responsible for establishing the metabolic rate of the body. In the hyperthyroid state it is essentially like being in a continual "revved up" state. Over time this chronic hyperactive state puts stress on the internal organs and heart. The severity of the disease depends on how much thyroid hormone is being produced.
Unkempt hair coat/ matted hair
poor stress tolerance
Heart murmurs/ rapid heart rate
Diagnosis: The diagnosis of this disease is based on clinical signs, palpation of an enlarged thyroid gland and increased blood levels of thyroid hormone (commonly called T4).
Treatment: Treatment for this disease is rewarding as most cats respond well to treatment if properly managed. The aim of treatment is to lower the levels of thyroid hormone being produced by the thyroid gland.
There are 3 treatment options: 1) Medication: Methimazole is a drug used to block the production of thyroid hormone. It controls but does not cure the disease and the medication has to be given for life. It comes in tablet form and is usually given twice daily. Most cats tolerate it well, however side effects are possible and bloodwork is essential to monitor for any adverse effects. 2) Surgery: It is possible to remove the hyperactive thyroid glands. The anaesthetic and surgical risk to the patient must be assessed carefully. Special care must also be taken during surgery so as not to damage the Parathyroid glands, which are important tiny glands that are associated with the larger thyroid glands. 3) Radioactive Iodine Therapy: This is now the treatment of choice as it is clearly the safest and most effective treatment. There are fewer complications than there are with methimazole therapy or surgery. A radioactive isotope is attached to the iodine molecule which is then selectively absorbed by the hyperplastic thyroid tissue and subsequently destroys the tissue. It usually only requires one treatment and side effects are rare.