Hyperthyroidism is the most common hormonal disease of older cats. It sends the whole body racing — but rest assured: properly monitored, it can be controlled very well, and your cat can keep an excellent quality of life.

What is hyperthyroidism?

The thyroid is a small gland in the neck that sets the body’s ‘speed’ — rather like an accelerator. In older cats it often starts producing too much hormone. The cause, most of the time, is a few small benign (harmless) nodules; very rarely, a cancerous tumour called a carcinoma. The result: the whole body runs in overdrive.

Which signs should alert you?

The most typical sign is a cat that loses weight while eating a great deal, sometimes more than before. We also frequently see:

  • Restlessness, nervousness, sometimes unusual aggression
  • A racing heart, increased thirst and increased urination
  • Vomiting or diarrhoea, a dull coat
  • More rarely, the opposite: a subdued cat with no energy

These signs settle in gradually and are easily put down to ‘a cat getting old’. A simple check-up can tell the difference.

How is the diagnosis made?

The vet relies on the symptoms, the examination (the enlarged thyroid can often be felt in the neck) and above all a blood test that measures the thyroid hormones. This work-up matters, because hyperthyroidism can mask another disease common at the same age — in particular chronic kidney disease (kidneys that no longer filter as well) — or be confused with diabetes.

How is it treated?

Several options exist, to be chosen together according to your cat:

  • A daily medicine, given for life: this is the most common option, and treatments designed for cats have improved greatly.
  • Radioactive iodine treatment: a single dose that cures the disease for good in the great majority of cases (carried out at a specialist centre).
  • A special diet low in iodine, or surgery, in certain situations.

The outlook is generally good: a properly treated and monitored cat can live a long, comfortable life. Only the rare cases of carcinoma are more delicate.

The key points: an older cat that is losing weight while eating a great deal should be examined. Hyperthyroidism is common, is picked up with a simple blood test and can be controlled well — regular monitoring is what makes all the difference.