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Feline Hyperthyroidism

The most common endocrine disorder of cats. A condition where the thyroid gland produces and secretes an excessive amount of thyroid hormone. In most cases, it is caused by one or more benign tumors or the thyroid gland.

Common Clinical Signs

  • Hyperactivity

  • Unkempt coat

  • Muscle wastage/weakness

  • Diarrhea

  • Weight loss

  • Increased appetite

  • Increased vocalization

  • Vomiting

  • Behavioral Changes:

    • Anxiety, nervousness, irritability,​ out of box urination/defecation.

How is it Diagnosed?

  • History

  • Physical Examination

  • Routine Laboratory Testing

  • Elevated thyroid hormones

  • Palpating an enlarged tumor in the neck region.

Treatment Options


for Life

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Special Diet

For Life

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Single Injection

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Medication for Life

Yup, FOR LIFE....Have you pilled a cat lately?

To medically manage hyperthyroidism your cat will need to receive a medication called methimazole (Tapazole or Felimazole are two brand names commonly used) every day (typically twice daily) for the rest of their lives.

methimazole blocks thyroid hormone secretion but the tumor continues to grow. 

Numerous side-effects such as vomiting, loss of appetite, severe facial itching, liver damage, drop in blood cell production and an increased susceptibility to infection make this treatment option less than ideal for long term therapy. 

Drug resistance (due to continued tumor growth), numerous side-effects mentioned avove, difficulty of pilling a cat, the long term cost of medication and periodic lab testing for the rest of your cat's life need to be considered when making your decision. 


Special Diet for Life


Must be the ONLY food source for the rest of your cat's life.​

  • No Treats! No Cat Grass!


  • No long-term studies for feeding this iodine restricted diet.


  • Your cat may not like the diet, or may quickly get bored with lack of variety.


  • Low in protein and can further promote muscle wastage. 


  • Difficult in multi-cat households where only one cat 'should' eat the diet (not advised for cats with normal thyroid function).​​


  • Not a CURE and not a great solution for most cats.


  • Click below for more information from Mark Peterson, DVM DACVIM the leading authority on feline hyperthyroidism.

Special Diet



  • The only other 'cure' for hyperthyroidism 

  • Requires anesthesia which can be very risky in a cat with hyperthyroidism due to potential heart disease, low body condition scores, hypertension, etc. 

  • Requires a skilled surgeon due to the location of the parathyroid glands. These 4 little glands (located within or near the thyroid gland) are responsible for calcium regulation. If these glands are damaged/removed during surgery this can result in a life-threatening decrease in blood calcium levels.

  • Multiple surgeries can sometimes be needed if both lobes of the gland are enlarged or if other thyroid tissue is involved. 

  • Small remnants of thyroid tissue are normally found spread throughout the neck and chest making them impossbile to pinpoint and remove. 

  • After unsuccessful surgical therapy, many cats are finally treated with radioiodine (I-131) and are cured.


Single Injection

95% Cure Rate with a single injection

Treatment of Choice and Considered the Gold Standard. 

No Anesthesia*


The thyroid gland uses iodine to make thyroid hormone. When we administer the radioactive form of iodine (I-131) the thyroid tumor (think of it as a 'greedy bully') that has taken over the thyroid takes up all the radioiodine leaving the normal thyroid tissue with nothing (don't worry, this is a good thing).

This radioactive form of iodine emits radiation, destroying the overactive thyroid tumor cells. Since the normal tissue wasn't able to take up the radioiodine it's left unharmed. It takes 3-6 months for the normal tissue to start functioning in a normal fashion again! Who doesn't love a happy ending?

What's the Catch? There really isn't one!

  • A very small number of cats may require a second treatment or need supplemental thyroid medication, but this is uncommon. 

  • Texas law, requires your cat  to be hospitalized until the (gamma) radiation levels are safe to go home (typically 4-5 days) following your cat's injection. 

  • Give us a call to schedule an appointment with Dr. Gandy to see if your cat is a candidate!

  • Some cats may require sedation for examination and to safely administer the injection.

Single Injection

Ready for a Cure?

Click above for our authorization forms and to schedule a consultation

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