Hyperthyroidism in Cats: What’s the Skinny?

(Photo by Chinda Sam)

A Note From Dr. John:

So you’re looking at Garfield wondering, “How in the world did he get this thin?” He vomits occasionally, but all cats do, right? And sure, he is 13 years old, but he eats like a pig and is always begging for more food.  You’ve tried 10 different diets, all with the same result.  What gives?  

This may not be as simple as inadequate nutrition or age-related weight loss. This scenario could be a classic presentation for a hyperthyroid cat.

What is hyperthyroidism?
The thyroid gland is responsible for producing the body’s thyroid hormone.  This hormone helps to regulate the body’s metabolism.  If you produce too little thyroid hormone, you are considered hypothyroid (a condition almost exclusively seen in dogs).  If you produce too much thyroid hormone, you are considered hyperthyroid.  

Being hyperthyroid is like having a metabolism that is in constant hyper-drive.  Though the thyroid gland is often hypertrophied (enlarged), the gland is very rarely cancerous.

What are the clinical signs of hyperthyroidism?
The most common clinical signs associated with this disease are weight loss, vomiting, and diarrhea despite having a good appetite.  The average age of diagnosis is around 13 years old but can vary.  Other signs often associated with the disease are increased thirst and urination, behavioral changes (begging for food, seeking attention, over-grooming, etc.), and increased respiratory rate.
How is hyperthyroidism diagnosed?
The good news about hyperthyroidism is that the diagnosis can easily be made by your veterinarian with a simple blood test.  General blood work to check kidney, liver, and other organ function at the same time is highly recommended.   Chest x-rays to evaluate heart size and shape are also recommended.  
So my cat is hyperthyroid- what’s next?
There are several options for treating hyperthyroidism.  I’ll touch on the basics, but ultimately, the decision on how to treat your cat will come down to a discussion that you have with your veterinarian.  Treatment will be based on a number of specific factors such as degree of hyperthyroidism, kidney function, cost, etc.. The mainstay of medical therapy for this disease is the daily use of the drug methimazole to limit the amount of thyroid hormone produced by the gland.  Other options are radiation therapy, surgery, and dietary management.  These options are usually only considered for cats after first evaluating their response to methimazole.  Again, make sure to discuss these options with your veterinarian.
What can I expect long term?
Hyperthyroidism can either be managed (by administering methimazole or with dietary management) or potentially cured (with surgery or radiation).  Regardless of the therapeutic route taken, once the hyperthyroidism is controlled, we would expect Garfield to regain some of those lost pounds.  We would also expect to see a decrease in other clinical signs noted prior to treatment- vomiting, diarrhea, and behavioral changes.  Depending on the therapeutic route taken, follow up action may be necessary.  This could include bloodwork, x-rays, and general physical exams. 

Our information is not intended to replace the advice of your veterinarian.  Do not use this information for diagnostic purposes. Always take your pet to your veterinarian to obtain a diagnosis and course of treatment.