Thyroid Problems

Information to help cats and dogs with symptoms of canine and feline thyroid problems

symptoms and causes of thyroid problems in cats and dogs

Select a Topic

  1. What are Thyroid Problems?
  2. What Causes Thyroid Problems?
  3. Diagnosing Thyroid Problems
  4. Help for Thyroid Problems

What are Thyroid Problems?

The thyroid gland consists of two small lobes shaped like butterflies with one each side of the windpipe (trachea) located in the neck. This gland produces thyroid hormones, thyroxine (T4) and triiodothyronine (T3). The primary function of these hormones regulates and maintains your pet’s metabolic rate which in turn affects their overall health and wellbeing.

Another hormone called thyroid stimulating hormone (TSH) which is produced by the pituitary gland, controls the production of the thyroid hormones. If the thyroid does not function properly, there may be a negative impact on your pet’s body weight, heart rate, skin and coat, digestive and reproductive health.

What Causes Thyroid Problems?

There are two types of thyroid disorders – hypothyroidism and hyperthyroidism.

Hypothyroidism affects mainly dogs, and rarely occurs in cats. When hypothyroidism occurs the thyroid gland is underactive and not enough thyroid hormone is produced, thereby slowing everything down. The exact cause is unknown but it may be caused by an auto-immune response in which the dog’s own immune system kills cells of the thyroid gland. Dogs that usually suffer from recurring skin problems have hypothyroidism.

Hyperthyroidism typically affects middle-aged to old cats (between 4 and 22 years of age), seldom developing in dogs. When hyperthyroidism occurs, the thyroid gland is overactive and produces too much thyroid hormone, speeding up the metabolism. The cause of hyperthyroidism has been established but dietary, immunological, genetic and environmental factors may also contribute to this disorder.

The common symptoms and signs of hypothyroidism include:

  • Weight gain or obesity
  • Lethargy and lack of energy
  • Dry skin and hair loss
  • Constipation
  • Slow heart rate
  • Anemia
  • Intolerance to cold
  • High blood cholesterol
  • Infertility
  • Seizures

Behavioral changes may also occur and include anxiety, depression, and hyperactivity, as well as being unfocused or passive.

The common symptoms and signs of hyperthyroidism include:

  • Weight loss even with an increased appetite
  • Diarrhea
  • Vomiting
  • Intolerance to heat
  • Dull, dry or oily coat with excessive shedding
  • Rapid/fast breathing
  • Increased water consumption accompanied by urination
  • Increased or decreased activity
  • Tremors

Behavioral changes such as nervousness, restlessness, hypersensitivity or stress may also occur.

Diagnosing Thyroid Problems

The diagnosis of a thyroid problem is based on the symptoms, thorough physical examination and review of your pet’s medical history. Certain tests such as a Baseline T4 Test, Baseline T3 Test, or TSH Stimulation Test will be performed if hypothyroidism is suspected. Your vet will choose the test most suited for your dog’s symptoms.

Generally, the TSH Stimulation Test will reveal whether your dog has a low T4 or T3 level. If hyperthyroidism is suspected, the diagnosis is based on the symptoms presented, enlarged thyroid gland (large enough that it can be felt), and high T4 levels.

Tests such as a CBC, serum chemistry, and urinalysis are performed if symptoms of other diseases such as kidney failure, liver disease, diabetes mellitus or heart disease are present with hyperthyroidism. In addition, tests such as the T3 suppression test, measurement of free T4 and thyrotropin-releasing hormone stimulation test may also be performed to confirm the diagnosis of hyperthyroidism.

Help for Thyroid Problems

Your vet may recommend the following standard treatments for hyperthyroidism in felines and these include radioactive iodine (I-131), anti-thyroid medication such as methimazole (tapazole) or surgery (thyroidectomy). These treatments have some adverse side effects such as liver damage, anemia, hair loss and lethargy, and cats with this problem should be kept away from pregnant women and children.

Treatment of hypothyroidism in dogs involves a daily dose of synthetic T4 hormone known as thyroxine (levothyroxine). Thereafter, follow-up blood tests will be taken in about six weeks to ascertain whether there is any improvement. This is life-long therapy but dogs usually go on to enjoy good health for the rest of their lives.

There are several things that you can do to prevent thyroid
problems and these include:
  • Feed your pet a natural, raw and well balanced diet that contains all the essential vitamins, minerals and nutrients
  • Ensure that your pet gets regular exercise
  • Take your pet to the vet for annual check-ups and monitor any abnormal physical and behavioral changes
  • If your pet suffers from a thyroid problem, become as knowledgeable as possible about this health problem


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