Thyroid Problems in Dogs

Dogs can have problems with their thyroid just like humans can.  Some of a dog’s symptoms are the same, but some are different.  Thyroid problems can be caused by too much thyroid hormone or by too little thyroid hormone.

Hyperthyroidism is when the thyroid produces too much thyroid hormone.  It is relatively rare in dogs.  Usually hyperthyroidism is the result of cancer in the thyroid gland. Because thyroid hormone speeds up the bodies processes, hyperthyroidism affects many of the organs in the body.  Symptoms include weight loss, vomiting, diarrehea, an unkempt appearance, increased appetite, increased thirst, increased urine production, and heart problems.  Treatment involves removing the cancer in the thyroid, if that is what is causing the problem.  Otherwise, medication can be given that blocks the action of the thyroid hormones.  In extreme cases, part of the thyroid may be removed or the dog may be given a dose of radioactive iodine, which destroys part or all of the thyroid.  Management of the hyperthyroidism depends on managing the medication the dog is on.  Thyroid levels have to be checked every two or three weeks until the most effective dosage is found.  If the dog has had part or all of his thyroid removed or destroyed, it is very important to give the dog his medicine every day.  Otherwise, he will develop hypothyroidism.

Hypothyroidism is when the thyroid doesn’t produce enough thyroid hormone. It is the most common thyroid problem in dogs.  According to Dr. Jean Dodd, autoimmune thyroiditis is responsible in approximately 90 percent of hypothyroidism cases.  This is where the body forms antibodies to the thyroid and gradually attacks it.  Eventually, enough of the thyroid has been attacked that it can no longer produce enough thyroid hormone to keep the dog healthy.  At this point, clinical signs of hypothyroidism appear.  These are weight gain, lethargy, generalized weakness, inactivity, mental dullness, excessive hair shedding, sore on the body, poor hair growth, recurring skin infections, intolerance to cold, and hair loss.  Not all dogs show all symptoms.

The most common treatment for hypothyroidism is supplementation of the T4 hormone.  This is given once or twice daily to the dog to replace the missing hormone in the system.  The first few months the dog is on thyroid hormone, he should be checked every sixty days for T4 level to determine the appropriate dose of medication needed.  The dog will require the medication for the rest of his or her life.  It is generally inexpensive and should not be a burden to administer.  Diet modifications, especially a reduction in dietary fat, may be recommended for the first phase of therapy.  This is especially true if the hypothyroidism has caused excessive weight gain in the dog.  It is important to help the dog loose the excessive weight and return to a more normal size.  Most dogs respond well to therapy, with activity levels and mental alertness returning to normal in a short time after the beginning of drug therapy.