Thyroid Hormone Deficiency in Cats

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Hypothyroidism in Cats

The thyroid gland is an essential gland in the body, producing a number of hormones, including T3 (liothyronine) and T4 (levothyroxine), both of which are required for normal metabolism in the body. Hypothyroidism is a rare condition in cats, with its occurrence being based on measurably lower than normal levels of thyroid hormones being produced and released throughout the body, and resulting slower metabolism along with other complications. This condition is usually seen in cats after thyroid surgery or radioactive iodine therapy has been given. In most cats this condition is transitory and does not require intensive therapy.

Symptoms and Types

This disease is rare in cats. Following are some of the symptoms presented in affected cats:

  • Lethargy
  • Inactivity
  • Mental dullness
  • Weakness
  • Weight gain
  • Unkempt appearance
  • Hair matting
  • Loss of hair (alopecia)
  • Delayed teeth eruption
  • Constipation
  • Low body temperature



  • Unknown etiology (origin)
  • Congenital disease
  • Iodine deficiency
  • Cancer
  • Side-effect of medical treatment, including surgery


A medical history and complete physical examination are important for the diagnosis of this disease. You will need to provide your veterinarian with a thorough history of your cat's health leading up to the onset of symptoms.

Finding the exact cause of hypothyroidism may require a thorough investigation. Routine laboratory testing will include a complete blood count, biochemistry profile, and urinalysis. Your doctor may be able to make an initial diagnosis based on the results of these tests, but endocrine testing is also an important panel for the diagnosis of hypothyroidism. The levels of T3 and T4 will be measured to determine if these are in the lower ranges. Radiographic studies may also be conducted to examine your cat internally for abnormalities that may be causing the dysfunction of the thyroid glands.

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