What is Feline Hyperthyroidism?

Thyroid glands play a vital role in regulating the cat body’s metabolic rate. Cats have two thyroid glands located on the underside of their neck. Hyperthyroidism is defined as the overproduction of thyroid hormone and a subsequent increase in metabolic rate. This is a common disease present in the adult cat population, especially those who are in their senior years. There are no correlation to any individual breed of feline having greater risk of developing the disease. The exact cause of Hyperthyroidism in cats has not yet been identified, although the role of dietary iodine continues to be investigated as an influencing factor.

Symptoms

A common symptom is weight loss despite having an increased/ravenous appetite, since the thyroid hormone is a major controller of the body’s metabolic rate. Vomiting and diarrhea may occur due to overeating and the changes in metabolism. Hyperactivity, vocalization and aggression are some common behavioral changes you may notice and cats often give the impression of being surprisingly active and energetic for their age. Unfortunately, although this activity is appealing, the negative effects that come with it are harmful on the heart, muscles, and skin. Treating the disease often causes a cat to “slow down” to a level that is more appropriate and is compatible with the functions of the organs (heart and muscles for example). Heart muscles can be affected to meet the increased metabolic demands as they become enlarged and thickened. Cats can develop a heart murmur associated with this.

How is the cause diagnosed?

A routine blood testing for thyroid hormone (T4) will help diagnose for hyperthyroidism. Routine bloodwork and urinalysis are necessary to assess the effects on the other organs and to screen for other serious illnesses like renal disease or liver disease since it could mask these diseases and make it difficult to treat them. Chest X-rays and sometimes echocardiograms to assess the effects on the heart from the disease are recommended. 

How is it treated?

There are two ways to manage hyperthyroidism as a disease:

• Daily Antithyroid Medication: Methimazole (Tapazole, Felimazole), given every 8-12 hours as prescribed for life. May take several weeks to restore normal thyroid function and blood work should be evaluated every 4-6 months. Wear gloves when administering the medication.
• Radioactive Iodine Treatment (iodine-131): Injected it will collect in the thyroid gland, destroying the abnormal tissue. It is a very effective (98% cure), very low-risk from treatment and it can only be given in hospitals that are licensed to handle the radioactive substance. The chance or recurrence in the future is less than 1%, and there are no daily medications to give thereafter. Normalizing the thyroid tissue can unveil underlying kidney disease and many specialists recommend a period of oral antithyroid medication and a recheck of kidney function to determine if a cat is a good candidate for permanent correction of hyperthyroidism with radioactive iodine. For more information please visit https://radiocat.com/

Conclusion

• Administer all medications as prescribed on time, even if your cat seems normal. Often this may be due to the positive effect of the medication.
• If you are giving your cat methimazole, watch for the symptoms of adverse effects (lack of appetite, inactivity, weight loss, and intense facial itching), stop the medication and call us!
• Realize that hyperthyroidism is a lifelong condition that does not get better on its own and that eventually causes life-threatening symptoms if not treated.
• Contact your veterinary team at (713) 461-3111 with any questions