Hyperthyroidism in Cats

What is hyperthyroidism in cats?

  • Feline hyperthyroidism is a common disease in middle aged to older cats.
  • It is caused by an enlarged and overactive thyroid gland(s) – usually a benign tumor that causes production of excessive thyroid hormone (T4).
  • Signs of an overactive thyroid can include:
    • Weight loss/muscle wasting
    • Increased appetite
    • Hyperexcitability
    • Increased vocalization day or night
    • Increased thirst and urination
    • Vomiting and/or diarrhea

How does hyperthyroidism affect the heart?

Effects on the heart (thyrotoxic cardiomyopathy) may include:

  • Rapid heart rate
  • Abnormal heart rhythm
  • Abnormal heart sounds (murmur +/gallop)
  • Thickening of the heart muscle
  • High blood pressure
  • Congestive heart failure (fluid in or around the lungs)

How is it diagnosed?

  • Physical exam findings may reveal an enlarged thyroid gland(s), thin body condition, abnormal heart sounds, poor coat quality, or muscle weakness.
  • A blood test demonstrating a high T4 level( too much thyroid hormone) confirms the diagnosis.
  • A small percentage of hyperthyroid cats will have a normal T4 level either because they are early in the disease process or because there is a concurrent illness suppressing the T4 level. In these cats, repeat measurement and/or other specialized thyroid hormone tests and/or imaging of the thyroid glands may be recommended to reach a diagnosis.

How do you treat hyperthyroidism in cats?

Treatment options include: