Hyperthyroidism In Cats

What Is Hyperthyroidism?

Roughly speaking, thyroxine (or T4) is a hormone that sets the rate at which many body processes run. That’s why an underactive thyroid (hypothyroidism) in a dog causes lethargy, poor hair growth and weight gain.

Thyroid problems in cats usually involve too much thyroxine, making many systems run too fast. The cause is typically benign enlargement of one or both thyroid glands.

What Are The Symptoms Of An Overactive Thyroid?

Cats with thyroid disease can have:

  • An increased appetite*
  • Weight loss*
  • Hyperactivity
  • Increased drinking
  • Poor coat condition*
  • Diarrhoea or vomiting
  • Heart Failure
  • Detached retinas & sudden blindness
  • Kidney failure may be caused by or just together with hyperthyroidism (both very common)
  • An occasional cat will have paradoxical lethargy and poor appetite instead

* Common.

The enlarged thyroid nodules usually cannot be seen, but can be felt by an experienced vet.

How To Treat Hyperthyroid Cats

First we need to confirm our suspicions, which is very easily done with standard feline blood tests.

Thyroid Surgery

It’s quite possible to remove one or both thyroid glands. It’s not our preferred option as removing a solitary enlarged gland usually only produces temporary relief, and removing both thyroid glands risks damaging the parathyroid gland at the same time.

Anti Thyroid Medicines

Most cats start here. Even if other options are advised, we will use medicines first to see what effect normalising the thyroid hormone will have. If the kidneys can’t cope with the change we can easily stop or reduce the treatment.

There are several good tablet options allowing for once or twice daily treatment. Once we start medication we need to retest to make sure we are giving the right dose.

The use of anti thyroid medicines in a transdermal skin ointment has fallen out of favour as we have come to realise these cats do not enjoy the same level of control or lifespan as other cats.

Don’t worry if you’ve had trouble with tablets before. We find most owners manage to find a way.

Radioactive Iodine Treatment

A single dose of I131 can normalise a cat’s thyroid hormone levels. This is especially attractive for cats that will be hard to medicate. Disadvantages are: cost, availability, the need to stay in a sealed environment and irreversibility.

Referral is possible in Adelaide for radioactive iodine treatment.

Iodine-restricted Diet

The latest option for treatment is the use of a controlled diet very low in iodine, an essential element for thyroxine production. This gives us a valuable choice for treating selected cats or improving thyroid control in difficult cases. Owners need to be extremely diligent not to allow any other foods to be consumed, and results show not all cats achieve normal thyroid levels.

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