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Hyperthyroidism in Cats
Overview

Hyperthyroidism in cats is a common endocrine (hormone) disorder in which the thyroid gland produces excess thyroid hormones. The condition affects about 10% of cats over the age of 10.  If left untreated, hyperthyroidism can contribute to significant health issues, such as heart disease, high blood pressure and kidney problems. However, the right approach can manage or even cure the condition, enhancing your cat’s quality of life and overall well-being.

A cat with hperthyroidism

What are the symptoms of hyperthyroidism?

The most common symptoms of hyperthyroidism in cats are:

  • Weight loss despite an increased appetite
  • Vomiting
  • Increased thirst and urination
  • Behaviour changes like restlessness, crying, or agitation
  • An unkempt coat or poor grooming habit

In more severe cases, hyperthyroidism can lead to heart disease, which may cause your cat to breathe rapidly or struggle with physical activity.

Early detection and treatment are the key to preventing serious complications and allowing your cat to return to their wonderful best.

Radioactive iodine treatment

Radioactive iodine is the only curative treatment for hyperthyroidism in cats. The treatment targets overactive thyroid tissue with a small dose of iodine, sparing healthy areas. It requires a brief isolation period afterwards.

Cat in an isolated ward

PROS

  • A curative treatment that is considered the gold standard
  • One treatment usually resolves the issue, avoiding ongoing medication
  • Minimally invasive, targeting only the thyroid and reducing side effects
  • Typically, more cost-effective in the long run compared to other treatments

CONS

  • Requires a week of isolation in a specialist facility due to radioactivity level
  • Unsuitable for some cats with underlying medical conditions
  • Dosage determination requires an experienced specialist team for the best outcomes

Cat Specialists Services offers a world-class radioactive iodine treatment facility specifically designed to create a stress-free environment that supports the well-being of cats during their stay.

Dietary management in cats

Dietary modification

PROS

  • Non-invasive treatment requiring only dietary changes
  • Useful for owners who prefer to avoid daily medications

CONS

  • Not a curative treatment; symptomatic relief only
  • Requires strict adherence, which is difficult for multi-pet
    households
  • Unsuitable for cats needing different food for other
    conditions

In the dietary management of hyperthyroidism in cats, iodine intake is restricted through targeted dietary management, effectively reducing thyroid hormone production. This helps to control some hyperthyroid symptoms.

Cat owner giving her cat medication

Oral medication

PROS

  • Widely available in tablets or liquid form
  • Non-invasive and effective if used consistently

CONS

  • Not a curative treatment; some symptomatic relief only
  • Ongoing medication and monitoring make this the most expensive option after 1-2 years of treatment
  • Prolonged use increases the risk of disease progression to the more serious thyroid carcinoma
  • Some cats are hard to medicate, causing stress for you and your cat

Oral medications control hyperthyroidism symptoms but don’t cure the condition, and long-term use may escalate costs and increase disease risk.

Surgery

A surgical procedure can remove the affected thyroid gland in cats with hyperthyroidism. This is rarely chosen due to the availability of less risky, more effective and less expensive treatments.

PROS

  • Offers a quick solution for patients needing immediate results
  • Potentially curative when other treatments are not viable

CONS

  • Not as reliable in curing the condition as radioactive iodine treatment
  • There are significant associated risks, including anaesthesia, surgical and post-surgical complications
  • Used mainly for cases where radioactive iodine is unsuitable, like severe heart disease
Hyperthyroidism and cats

A few facts about hyperthyroidism and cats

All mammals, including cats, have two thyroid glands in the neck, one on each side of the windpipe (trachea). These glands usually are about 4-8 mm wide and 10-20 mm long. Their primary function is to produce thyroid hormones like T4 (thyroxine) and T3 (triiodothyronine), which regulate metabolism—the process of turning food into energy.

In cats with hyperthyroidism, these thyroid glands enlarge, which can often be felt by gently touching the cat’s neck.

Hyperthyroidism causes the glands to produce too much thyroid hormone, which affects almost every part of the cat’s body.

Thyroid hormones are crucial in regulating the body’s metabolic rate or how quickly the body uses energy from food. These hormones influence the function of every cell and organ, including the heart, digestive system, and muscles. In hyperthyroid cats, the metabolic rate increases, which explains why affected cats often lose weight despite eating more than usual.

In addition to weight loss, excessive thyroid hormone levels can also:

  • Speed up or slow down the heart rate
  • Raise or lower body temperature
  • Increase the speed at which food passes through the digestive tract

Hyperthyroidism in cats was first reported only about 40 years ago, it is now recognised as the most common hormonal disorder in cats worldwide. Interestingly, this condition is more prevalent in cats than other domestic animals, but the reasons for this are not entirely understood.

Despite extensive research, the underlying cause of hyperthyroidism in cats remains unclear. However, several factors may contribute to the development of the disease, including:

  • Iodine deficiency or inconsistent iodine levels in the diet
  • Long-term exposure to thyroid-disrupting chemicals, such as BPA (found in some plastics) and
  • PBDEs (used in flame retardants)
  • Cats may be more vulnerable to these chemicals due to their grooming habits, increasing their exposure to contaminants.

Although we don’t fully understand why hyperthyroidism occurs more frequently in cats, it’s clear that this condition can have serious health effects. Understanding how the thyroid glands work and the impact of thyroid hormones on a cat’s body can help cat owners recognise early symptoms and seek treatment quickly.

Read Part 2 here

Are you worried about your cat’s health?

If you are concerned about your cat, please reach out to our friendly team. Call us on 1300 228 377 or fill out the contact form below. In an emergency, please contact your local vet.

For vets – to refer a patient or book a telehealth consultation, please call us on 1300 228 377, book through the portal or fill in the form.

Patient Stories

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Each patient faced unique challenges, and it was our honour to offer high-quality care and help them regain strength and happiness. We value the deep bonds with cats and their owners, knowing the difference we make in their lives.

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Contacting Us

Pet Owners
If you would like to talk about treatment for your cat, call us on 1300 228 377 or fill in the form.
In an emergency, please contact your local vet.

Vets and Nurses
To refer a patient or book a telehealth consultation please call us on 1300 228 377, book through the portal or fill in the form. For advice calls, please see the guidelines here.

1300 228 377
1-15 Lexington Rd,
Underwood, QLD, AU, 4119
Monday-Friday: 8 am-6 pm
Saturday/Sunday - Closed

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