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Hyperthyroidism in Cats: Causes, Symptoms, Treatment, and Prevention

If your feline friend is suffering from hyperthyroidism, you may be struggling to find the right treatment for them. Hyperthyroidism is a common condition in older cats that results in the overproduction of thyroid hormones, which can affect various organs and systems in the body.

Symptoms may include weight loss, increased appetite, restlessness, vomiting, diarrhea, and heart problems. To diagnose hyperthyroidism, your veterinarian may perform blood tests and other diagnostic procedures.

Treatment options may include medication, surgery, radioactive iodine therapy, or dietary therapy. However, not all treatments are suitable for every cat, and some may have side effects or complications that can worsen their health.

It's important to understand what causes hyperthyroidism in cats, how it affects their health, and how it can be prevented or managed.

In this article, BestForPets'll provide you with information on hyperthyroidism in cats, including diagnosis, treatment, possible complications, and prevention. We'll also provide you with resources for further reading or assistance on this topic.

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icon Reviewed & Fact - Checked by

Deborah R. Fletcher (DVM)

Veterinarian

The information provided is current and up-to-date, in line with the latest research conducted in the field of veterinary medicine.

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What Causes Hyperthyroidism in Cats?

What Causes Hyperthyroidism in Cats?

Your cat’s thyroid gland is a small gland located in the neck. Thyroid hormone regulates metabolism and other physiological functions. A feedback mechanism between the pituitary gland and hypothalamus in the brain regulates the amount of thyroid hormone.

The most common cause of hyperthyroidism in cats is benign thyroid tumors that produce excessive thyroid hormone. These tumors are called adenomas and are typically present in both thyroid lobes. They are not malignant and do not spread to other organs.

Other potential causes of hyperthyroidism in cats include cancerous tumors, iodine deficiency or excess, dietary and environmental factors, among others. However, these causes are rare and not well understood.

Excess thyroid hormone can have various effects on the body’s organs and systems, including:

  • Heart: It increases heart rate, blood pressure, and oxygen demand. It can also cause abnormal heart rhythms, enlargement of the heart muscle, or heart failure.
  • Kidneys: It increases blood flow to the kidneys and urine output. It can also cause dehydration, electrolyte imbalance, or kidney damage.
  • Liver: It increases metabolism of fats and proteins in the liver. It can also cause liver inflammation or dysfunction.
  • Muscles: It increases breakdown of muscle tissue and protein. It can also cause muscle weakness or wasting.
  • Skin: It increases blood flow to the skin and the hair growth cycle. It can also cause skin thinning or hair loss.
  • Nervous system: It increases activity of the nervous system and sensitivity to stimuli. It can also cause anxiety, nervousness, irritability, or aggression.

How Is Hyperthyroidism in Cats Diagnosed and Treated?

How Is Hyperthyroidism in Cats Diagnosed and Treated?

A veterinarian can diagnose hyperthyroidism in cats through blood tests, physical examination, and other methods. Blood tests check thyroid hormone levels (T4) and other parameters, including kidney and liver function, blood count, etc.

Physical examination looks for symptoms such as weight loss, increased appetite, elevated heart rate, enlarged thyroid gland, etc. Other techniques include ultrasound, scintigraphy, and biopsy.

The primary treatment options for feline hyperthyroidism are:

1. Medication

This involves administering methimazole (Tapazole), which inhibits thyroid hormone production in your cat. Methimazole is typically administered orally as a tablet or liquid or transdermally as an aural lubricant.

While the medication is effective at reducing thyroid hormone levels, it doesn’t cure hyperthyroidism and can cause adverse effects, including vomiting and appetite loss. Methimazole may also cause vertigo, irritation, lethargy, blood disorders, or liver problems.

Regular blood tests are required to monitor thyroid levels and possible adverse effects. Typically, methimazole is administered for life or until another treatment option is selected.

2. Surgery

This requires surgical removal of the thyroid gland or a portion of it, which is a permanent and effective treatment for hyperthyroidism. However, surgery has risks and side effects, including general anesthesia and an overnight hospital stay for your cat.

There’s a possibility of hemorrhage, infection, nerve injury, and tumor recurrence. After surgery, your cat may also develop hypothyroidism or hypocalcemia, requiring hormone replacement therapy.

3. Radioiodine therapy

This involves injecting your cat with a radioactive form of iodine (I-131) that selectively destroys aberrant thyroid tissue. This treatment is safe and effective without the need for surgery or medication.

However, it’s expensive and in limited supply. Your cat will be hospitalized for several days to weeks until the radiation level is deemed safe. After treatment, your cat may also develop hypothyroidism, requiring hormone replacement therapy.

4. Dietary treatment

This involves serving your cat a special diet with minimal iodine content. This decreases the quantity of iodine available for thyroid hormone synthesis, consequently decreasing thyroid hormone levels in hyperthyroid animals.

This treatment is straightforward and non-invasive, requiring neither medication nor surgery. However, it’s not very effective at reducing thyroid hormone levels, and some cats may find it unsuitable or unpalatable.

In addition, your cat must only consume this diet and avoid other foods or indulgences that may contain iodine.

What Are The Complications Of Hyperthyroidism In Cats?

What Are The Complications Of Hyperthyroidism In Cats?

Hyperthyroidism in cats can result in secondary complications such as heart disease, kidney disease, hypertension, ocular problems, skin problems, etc. If these complications are not detected and treated promptly, they can be life-threatening.

Some symptoms and effects of these complications include:

1. Cardiac disease

Hyperthyroidism can increase heart rate, blood pressure, and oxygen demand. It can also cause abnormal cardiac rhythms, heart muscle enlargement, and heart failure. These conditions can cause difficulty breathing, dizziness, collapse, and even sudden death.

2. Renal disease

Hyperthyroidism can increase kidney blood flow and urine production. It can also cause dehydration, electrolyte imbalance, and kidney injury. These conditions can result in increased thirst and urination, weight loss, vomiting, lethargy, and kidney failure.

3. Hypertension

Hyperthyroidism can cause hypertension, which can damage blood vessels and organs such as the eyes, brain, and kidneys. This can result in blindness, stroke, seizures, coma, or death.

4. Ocular problems

Increased blood pressure caused by hyperthyroidism can damage blood vessels in the eyes and cause an increase in ocular pressure, which can harm the optic nerve. These conditions can cause vision loss, glaucoma, retinal detachment, and other eye problems.

5. Skin problems

Hyperthyroidism can increase blood flow to the skin and the hair growth cycle. It can also cause thinning of the skin and hair loss. These conditions can result in poor coat quality, chapped skin, irritation, infections, and more.

How To Prevent Hyperthyroidism In Cats?

How To Prevent Hyperthyroidism In Cats?

Preventing or delaying hyperthyroidism in cats can involve reducing or avoiding risk factors that may contribute to its development.

Some methods for reducing your cat’s exposure to iodine and other thyroid-disrupting substances include:

  • Feeding your cat a well-balanced, high-quality diet that is low in iodine and free from additives that may interfere with thyroid function.
  • Avoiding providing your cat with tinned foods that have a fish flavor and may contain high levels of iodine or other contaminants that may interfere with thyroid function.
  • Avoiding using plastic food dishes or containers that may leach thyroid-altering compounds, such as bisphenol A (BPA) or phthalates.
  • Avoiding exposing your cat to household products or furniture that may contain flame-retardant compounds (PBDEs) that may have an impact on thyroid function.
  • Avoiding exposing your cat to pesticides and herbicides that have the potential to affect thyroid function.

Some methods to ensure your cat’s optimal health and well-being include:

  • Providing your cat with a stress-reducing and relaxing environment that is clean and comfortable.
  • Providing your cat with regular veterinary check-ups, vaccinations, parasite control, dental care, etc., to prevent disease and infection.
  • Providing your cat with enough physical activity and mental stimulation to maintain their health and happiness.
  • Providing your cat with plenty of fresh water and a moist diet to promote hydration and kidney health.
  • Providing your cat with love and care to strengthen your bond with them and enhance their quality of life.

What To Avoid When Feeding A Hyperthyroid Cat?

What To Avoid When Feeding A Hyperthyroid Cat?

1. Avoid feeding your cat foods made from fish

A 2000 study found that cats who preferred tinned cat food with the aromas of fish or liver and giblets had a higher risk of hyperthyroidism.

Fish and other marine organisms have higher iodine concentrations than other diets, which may be a contributing factor, but it’s not certain that iodine content is the sole issue. If you’re concerned about your cat’s diet, consult your veterinarian.

2. Be aware that the majority of fish contain toxins, including PBDEs

These flame-retardant compounds were widely used in the past and can disrupt thyroid function. A study published in 2017 found that hyperthyroid cats had higher PBDE blood levels than healthy cats. To avoid this, look for BPA-free canned food for your cat.

3. Avoid feeding your cat soy, as it can interfere with optimal thyroid function

When researchers fed healthy adult cats a soy-containing or soy-free diet for three months, they discovered that the soy-fed cats had “significantly higher total thyroxine (T4) and free thyroxine (fT4) concentrations, but unchanged total triiodothyronine (T3) concentrations.”

The soy-based diet had a small but significant effect on the body’s production of thyroid hormone.

4. Select a diet low in iodine

Iodine serves a role in the production of thyroid hormones, so a cat with hyperthyroidism should consume a diet deficient in iodine to help prevent the overactive thyroid glands from producing even more thyroid hormone.

Hyperthyroidism in cats can be managed with the right diet, and this article on “Best Cat Foods For Hyperthyroidism” can help you choose the right food for your feline companion to support their health.

Conclusion

Hyperthyroidism in cats is a common condition that causes the thyroid gland to produce too much thyroid hormone, which can lead to various symptoms such as weight loss, increased appetite, restlessness, vomiting, diarrhea, and heart problems.

Diagnosis and treatment options include blood tests, medication, surgery, radioactive iodine therapy, or dietary therapy. However, it’s important to note that not all treatments are suitable or effective for every cat and some may have side effects or complications.

To prevent or manage hyperthyroidism in cats, it’s important to understand its causes, how it affects their health, and what steps can be taken.

In this article, we’ve provided information on hyperthyroidism in cats, including its diagnosis and treatment options, as well as possible complications and prevention methods.

BestForPets hope this article has been helpful in understanding hyperthyroidism in cats and how to manage it. If you have any questions or concerns, please feel free to leave a comment or contact us for further assistance. Thank you for reading!

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Dr. Linda Wilson

Dr. Wilson has devoted her professional life to the treatment of cancer in dogs, cats, horses, ferrets, rabbits, and other exotic species. She has more than 15 years of expertise in the area and is dedicated to giving her patients the best treatment possible.

Veterinarian (DVM) Dr. Linda Wilson

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