Hyperthyroidism is the most common endocrine (hormonal) disease in older cats. It is caused by an enlargement of the thyroid gland (next to the windpipe). 97-99% of cases are caused by a benign increase in the thyroid tissue. Thyroid hormone regulates your cats metabolism so common signs of an increase in hormone include: weight loss despite eating more (many cats are ravenous!) drinking more, urinating more, behaviour changes (hyperactivity, aggression), heart disease (fast heart rate, audible murmur). A few cats will have vomiting/diarrhoea.

Less commonly the opposite will occur – 1 in 10 cats with hyperthyroidism will be off food and lethargic. If hyperthyroidism is suspected on physical examination the next step is a blood test to measure the thyroid hormone level in the blood.

Treatment Options:

  1. Oral Medication: pills once or twice daily (lifelong).
  2. Topical: if you have trouble administering pills you can request a gel to be compounded by a
    pharmacy which is rubbed onto the ear (lifelong).
  3. Diet Hills y/d: a new prescription diet which has a restricted level of iodine to decrease thyroid hormone production (lifelong).
  4. RAI (radioactive iodine): RAI treatment destroys all abnormal thyroid tissue (curative in almost all cats).

The major disadvantage of pills, gels and prescription diet are that they are lifelong whereas RAI is a one-off curative treatment in most cats; it is however quite expensive and requires 7 days of hospitalised isolation. The major issue with a prescription diet is that ONLY this food can be fed to your cat (no treats!) Multicat households are not ideal as healthy cats and affected cats may switch meals.