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Thyroid Disease

Thyroid – Thyroid disease is common in dogs and cats.  Interestingly, 99% of the thyroid disease in dogs is hypothyroidism (low thyroid function), and 99% of the thyroid disease in cats is hyperthyroidism (high thyroid function).  The following articles address these issues.


Hypothyroidism means that the thyroid gland has quit producing enough thyroid hormone.  This is usually caused by one of two things:


The immune system has destroyed his or her thyroid, or

The thyroid gland has just atrophied (gradually disappeared).


This disease can be seen in any breed, but many breeds are predisposed.  They include Golden Retrievers, Dobermans, Dachshunds, Irish Setters, Miniature Schnauzers, Great Danes, Poodles, and Boxers. 


Most dogs develop this disease between 2 and 9 years of age with the large and giant breeds developing hypothyroidism commonly at 2 – 3 years of age. 


Clinical signs in dogs are all related to a decrease in circulating thyroid hormone.  This hormone regulates metabolism and therefore a lack of it can affect almost any organ system.  Clinical signs are often very slow to develop and many people don’t notice a problem for months.  Symptoms we see are found in the following categories:


Mental Status and general attitude:  Your pet may have mental dullness, lethargy, exercise intolerance or an unwillingness to exercise.


Weight gain: Most hypothyroid dogs gain weight without an increase in food consumption.  Most of us can remember how our metabolism changed during the college years and those pounds showed up.  A similar slow down in metabolism caused that same type of weight gain in dogs with low thyroid function.


Cold natured:  Hypothyroid dogs can’t keep their temperature up easily and thus are often described as “heat seekers”.  They want to lay next to the stove or under covers in many cases.


Skin problems:  This is the most common sign that owners notice and that we see.  The classic presentation is a symmetrical area of hair loss, scaling, dry coarse hair coat, and dullness to the coat over the trunk of the body.  It is usually not itchy unless secondary problems have occurred, and the head and legs are usually spared these changes.  The exception would be the large and giant breeds in which we see these changes on the legs as well.  Some dogs develop a “rat tail” in which most of the hair on the tail is lost and hair is often very slow to regrow after grooming (our first hint in some cases is an area that we shaved for surgery does not regrow hair!).  The skin often becomes dark with pigment and becomes very thickened to the touch.  This is often noticeable in the facial area to many people. 


Reproductive problems:  Females that are hypothyroid often fail to come in heat; and males can be infertile. 


Heart problems:  Many hypothyroid dogs have a slow heart rate and poor circulation.  Their skin may feel cool to the touch.  Dogs that are hypothyroid often have very high cholesterol levels.  Occasionally they will develop cardiovascular disease just like humans do!


Eye problems:  Some dogs develop fatty cholesterol deposits on their corneas which look like white plaques.  Once again this is due to the very high blood cholesterol that we see.


Nerve and muscle problems:  Many hypothyroid dogs become stiff and sore, develop muscle atrophy, and even shuffle their feet, wearing off the tops of their toenails.  Weakness of the muscles of the eyelids result in droopy eyes that many people will notice as a problem. 


Intestinal problems:  Some hypothyroid dogs develop a low grade chronic diarrhea. 


Diagnosis of hypothyroidism requires a blood test.  We usually start with a simple measurement of thyroid hormone level called T4.  However, we occasionally have to run a thyroid panel to diagnose early cases of the disease. 


Treatment is easy and we start with thyroid medication two times daily.  After a few months of medication we like to recheck the thyroid levels 6 – 8 hours after you have given the medication.  This may allow us to reduce the dosing to once a day.  About ½ of the dogs can go to once a day medication while the other ½ need it two times a day.  It is important to remember that we are not “curing” the thyroid disease.  Your pets’ thyroid will NEVER begin working like it should.  You will need to medicate your pet FOREVER.  Thankfully, the medication is inexpensive and will not impact your budget! 


Please call us with any questions that you think of.  We would be glad to discuss this or any other problem that you’re other pets might have.


Hyperthyroidism is the most common endocrine disorder in cats.  It is seen typically in older cats and many people just think it is old age.  Cats with this problem will eat a lot, have large volumes of stool, and gradually lose weight – becoming very thin.  The cause of this problem is that the thyroid gland(s) hypertrophy (enlarge) and start to produce far too much thyroid hormone.  This hormone is needed in small quantities for normal health, but in large quantities causes devastating problems.  Left untreated, hyperthyroidism and the problems that is causes will prove to be fatal.  Treatment is aimed at lowering the level of thyroid hormone being produced.  Three methods are used:


  1. A drug called Tapazole that is given once or twice a day blocks the production of thyroid hormone.  This often works well but we have three potential problems.  First, it must be given once or twice a day FOREVER.  A lot of cats decide they would rather pass on the pill.  Second, it is costly in the long run. Third, potential side effects are many.  We recommend that cats on long term Tapazole have blood work checked weekly until the thyroid levels are normal and then at least every 6 months to monitor for toxic signs and lack of effectiveness.
  2. Surgery is the most cost effective way to treat cats with hyperthyroidism.  After a short round of medication to lower hormone levels and blood work to evaluate other organ functions, we surgically remove one or both of the thyroid glands – depending if one or both are involved.  We are one of the few hospitals that offer this surgery.  It is a meticulous procedure, tiny blood vessels must be tied off, nerves near the thyroid protected, and care must be taken to preserve the tiny parathyroid gland that lies on top of the thyroid gland, regulates calcium levels, and must not be removed during surgery.  After surgery, if both thyroids were removed, we will keep kitty to monitor his or her calcium levels for 2 – 3 days.  After suture removal in 10 days, most cats go back to a normal life and interestingly, even with both thyroid glands totally gone in most cases, we never have to supplement them with thyroid replacement.
  3. Radioactive iodine is another way to treat hyperthyroid cats.  This is the way humans are treated with this disease; however, we don’t routinely recommend it.  It is expensive, requires taking your pet to a university facility – OSU, and leaving him there for 3 – 4 weeks.  We do recommend this occasionally when an animal has what is termed “ectopic” thyroid tissue in their chest which is not surgically approachable. 
  4. Recently, in 2010, a new diet was introduced to treat hyperthyroidism. It is made by Hills and is called Y/D.  It has a very restricted level of iodine in it, which is the element that is used by the thyroid gland to produce thyroid hormone.  Research has shown this diet to be very effective in treating hyperthyroidism, and in the future it may be our treatment of choice for this disease.  We have been very pleased so far.   


In short, hyperthyroidism is a very treatable disease today.  If your cat has been diagnosed with this disease, we typically will recommend a change to the diet Y/D as long as he or she will eat it and can tolerate the food.  In the event that we find Y/D is not an option for your kitty, we will usually start oral medication for a while followed by surgery to remove the thyroid glands.  This will allow for faithful companion to live a much longer and healthier life.

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