Hyperthyroidism occurs when too much thyroid hormone is created and released from the thyroid glands. The reason the gland secretes more hormones is that the gland enlarges and becomes overactive. Generally, this is from benign (non-cancerous) growth. Although not cancer, this overactive thyroid gland tissue can cause life-threatening problems. It is very rare in dogs but is actually quite common in cats. In fact, it is the second most common disease that we see in cats over 10 years old (kidney disease is the most common.)

  • Symptoms:

Generally, the signs of the disease are directly related to the function of the thyroid hormone excess. It is rare that you will notice a thyroid mass at home. The classic signs of hyperthyroidism are weight loss, increased appetite, and hyperactivity/restlessness.

Behavioral changes are a very common cause of why the cat or dog was brought to the office. Some other signs include diarrhea, patchy hair loss, matted fur/unkempt coat, excessive grooming, increased thirst/urination, vomiting, aggression, anorexia, and dehydration.

  • Treatments:

There are 3 treatments for this disease: Surgery, medication, and radioactive iodine.

  • Surgery:

This is the most invasive treatment, is quite costly, and carries a high rate of recurrence. It can also cause another hormonal disease called hypoparathyroidism if both thyroid glands are removed. Given all of that, it is not a recommended treatment unless (1) you can’t give medication or (2) you don’t live near a facility that can give the radioactive iodine.

  • Medication:

Anti-thyroid medication (methimazole) does not cure hyperthyroidism. They block the ability to form functional thyroid hormone. This medication is both short-term and long-term and is relatively inexpensive.

  • Radioactive Iodine:

This is often the most successful means of treatment for hyperthyroidism in cats. Radioactive Iodine (I131) is given via a simple injection. It damages the thyroid hormone-producing cells without damaging the surrounding tissues. Unfortunately, our hospital does not offer this treatment, but there are several facilities close by that do upon referral.

  • Prevention:

This disease cannot be prevented, but the earlier the detection, the more likely a good outcome for both dogs and cats. Annual examination includes a palpation of the thyroid gland areas. Annual lab work for both dogs and more importantly cats include a T4 test that might find subclinical hyperthyroidism. Knowledge of the symptoms and examination if they occur are also vital for early detection.