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Hyperthyroidism

Hyperthyroidism is the most common endocrine (hormone) disorder in cats. It is a disease caused by excessive amounts of circulating thyroid hormone (thyroxin) produced by the thyroid gland. The gland enlarges and produces a swelling in the neck - a thyroid nodule. The disease is mainly found in cats 9 years and older.

Signs of hyperthyroidism:

Aggression
Diarrhoea (diarrhea)
Hyperactivity - cat is restless and irritable, paces
Increased heart rate
Increased volume of faeces (feces)
Panting or difficulty breathing
Polydipsia - drinking increased amounts of water
Polyphagia - excessive hunger and food consumption
Unkempt appearance
Vomiting
Weight loss

The work of the heart is increased at a time when the heart is less strong. A form of cardiomyopathy occurs that can lead to congestive heart failure.

Blood tests for thyroid levels (T3 and T4) will establish a diagnosis.

Treatment is directed at returning the cat to a normal thyroid status. There are three different treatments that can be used.

Anti-thyroid drugs - Tapazole (Methimazole)
Surgery to remove the thyroid gland
Radioactive iodine at a referral center

References

Carlson DG & Giffin JM, Cat Owners Home Veterinary Handbook, New York: Howell Book House, 1995

Tilley LP & Smith FWK, The Five Minute Veterinary Consult - Canine and Feline (2nd Edition), Philadelphia: Lippincott Williams and Wilkins, 2000

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