Hyperthyroidism in Cats

Hyperthyroidism in Cats : Signs, Symptoms, & Treatment

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Jacquelyn Pica

Researched & Written by

Jacquelyn Pica

At EasyPet, we are committed to presenting the most accurate and up-to-date information to assist you in your pet care journey. When appropriate, we consult licensed and practicing veterinarians to fact-check our professionally written articles.

Like humans, cats, too, suffer from thyroid disorders.

The excessive production and concentration of thyroxine or T4 hormone in the bloodstream causes hyperthyroidism in cats.

One of the most common glandular disorders in cats, hyperthyroidism can occur in any breed and affect both male and female felines.

The disorder is rarely seen in cats younger than 10 years of age and is common in senior cats above 12 years.

Thyroid Gland in Cats

Unlike humans, cats have two 2 thyroid glands – left and right – that regulate the body’s metabolism through the production of thyroxine hormone.

The thyroid gland produces thyroxine in response to stimulation by the pituitary gland. The hormone is responsible for accelerating chemical processes within cells, particularly related to metabolism.

In a cat suffering from hyperthyroidism or glandular disorder, one or both glands may be involved, resulting in the overproduction of thyroid hormone. It is T4 hormone that regulates the speed of all the body processes.

Overproduction of thyroxine pushes the cells and body into overdrive and raises the metabolic rate, resulting in faster metabolism, rapid burning of energy, and quicker weight loss despite having a good appetite and increased consumption of food.

As a result, the body’s metabolic rate increases, causing complications in the form of anxiety, weight loss, and diarrhea, among other symptoms.

Hyperthyroidism is the most common hormone abnormality in cats, which is a form of overactive thyroid glands, resulting in the overproduction of thyroid hormone.

Since thyroid hormone regulates most body processes, too much production of the hormone causes dramatic clinical changes in the body. The kitty may become seriously ill.

Fortunately, hyperthyroidism in cats can be treated successfully if diagnosed early.

Hyperthyroidism in Cats Symptoms

Hormone abnormality in cats affects middle-aged and older kitties. It is rare in cats less than 10 years of age though can not be ruled out. A wide variety of signs can develop in cats, some of which can become complicated, if ignored.

Vets also use the word thyrotoxicosis to refer to the enlargement of thyroid glands. A benign or non-cancerous tumor, known as adenoma, may also contribute to the disorder. However, in rare cases, overproduction of thyroid hormone could be triggered by malignant tumors, or thyroid adenocarcinomas.

Cat Drinking Water

The most common signs of hormone abnormality in cats include:

  • Rapid weight loss despite increased appetite
  • Increased thirst
  • Poor coat and rapid fur loss
  • Restlessness or irritability
  • An increased heart rate or rapid breathing
  • Mild to moderate diarrhea/vomiting
  • Poor body condition
  • Thickened nails
  • Unkempt appearance
  • Polyuria or increased urine
  • Difficulty breathing
  • Aggression
  • Hyperactivity
  • Enlarged thyroid gland

Uncontrolled and untreated hyperthyroidism can stimulate the heart rate and causea strong contraction of the muscular wall of the heart.  Gradually, hyperthyroidism in cats may cause enlargement and thickening of the left ventricle, compromising with the normal functioning of the heart. This could even lead to heart failure.

Hyperthyroidism in Cats Diagnosis

Diagnosis requires careful examination of thyroid glands, which usually enlarge with hyperthyroidism. However, there may be no obvious signs of gland enlargement in some cats. This could be due to the placement of the overactive tissue in an unusual site.

Some of the signs of feline hyperthyroidism are similar to those of chronic liver disease, renal failure, and cancer. However, routine lab checks and thyroid function tests can help rule out these cat diseases.

While abdominal ultrasound may help in the diagnosis of an underlying renal disease, the vet may perform thoracic radiography and echocardiography to determine the severity of myocardial disease.

Vets perform thyroid gland scintigraphy to confirm hyperthyroidism in cats. The diagnostic test helps determine the location of abnormal thyroid tissue. The vet may conduct a blood test to measure T4 and T3 hormones.  Ideally a measure of the T4 hormone concentration is appropriate to confirm a diagnosis. Your kitty’s blood pressure and heart rate may be checked. Though thyroid problem may influence these , their measurement have no direct connection with the diagnosis.

If the blood tests show a high concentration of T4, it confirms the diagnosis of hyperthyroidism.

In rare cases, T4 levels may be normal, especially in the initial stages, making it challenging for vets to diagnose the glandular disorder in cats.

Since hyperthyroidism can predispose your furry friend to other medical conditions, the vet may need to evaluate her general health to get an overall picture of your cat’s health.

Checking Cat's Heartbeat

Hyperthyroidism in Cats Treatment

Kitties with serious heart disease and hyperthyroidism may require treatment for both diseases.  Hyperthyroidism in cats may require:

  • Oral anti-thyroid medications for a lifetime
  • Radioactive iodine treatment – intravenous injections of radioactive iodine that target abnormal thyroid cells
  • Surgical removal of thyroid glands in rare cases

Consult your feline’s vet before starting with any medication regimen for the safety of your cat health. Avoid starting on any medication therapy on your own, without consulting the doctor.

Check your kitty’s blood thyroid hormone levels at least once a year to keep your feline from any cat disease or disorder.

Hyperthyroidism in Cats Diet

Some studies also suggest that feeding your cat a diet low in iodine can help with hyperthyroidism. In another article, we explore that more in depth and discuss the best low iodine cat food in the process.

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