Hypothyroidism in the dog, where the thyroid gland is not secreting normal amounts of thyroid hormone, is the most common endocrine gland disorder in the dog.  The endocrine glands are listed below...

 

 

All of these tissues secrete chemical substances called hormones that have a profound effect on certain "target" tissues.  But of all those glands and hormones, the thyroid gland is considered the Master Gland.  If the thyroid gland is malfunctioning, every cell in the body is affected.  No wonder dogs, properly diagnosed with hypothyroidism and placed on appropriate thyroid hormone supplements, will look, act and feel so much better than before treatment.SIGNS

Most dogs show signs of hypothyroidism between 3 and 5 years of age but diagnosis isn't made in some dogs until they are years older.  Males and females seem to be equally affected.  Routine testing of young dogs is not commonly done.  Some veterinarians believe that if a dog has not acquired Hypothyroidism by 5 or 6 years of age, the odds are good that it will never be a problem for that individual.  (Cats rarely acquire hypothyroidism but have more trouble with hyperthyroidism, especially older cats.)  One of the most commonly seen signs that a dog may have insufficient secretion of thyroid hormone is weight gain with apparently little food intake.  Any overweight pet should be checked for Hypothyroidism.  (See this page for tips on how to get a pet to lose weight.) In long-standing cases there often is lack of proper hair coat and even hair loss.  This loss generally displays a pattern over the lumbar area on both sides, sparse hairs on the back of the rear legs and lack of hair along the abdomen.  The coat tends to lack luster and the finer hairs of the undercoat may be missing entirely.  Most dogs with hypothyroidism lack energy, prefer warm environments and have poor exercise tolerance. Of great concern to breeders is the fact that dogs with hypothyroidism may be infertile and many breeders have their dogs tested for thyroid function prior to breeding; in dogs with a poor breeding history, hypothyroidism often is the culprit.

 

DIAGNOSIS

If the physical exam or history indicates probable Hypothyroidism, the veterinarian will take a blood sample and have one or more tests run. The most common tests for thyroid function are T4 (the main Thyroid hormone) and canine TSH (Thyroid Stimulating Hormone from the Pituitary Gland). Some veterinary laboratories now recommend TgAA (Thyroglobin Auto-antibody) analysis be done because it identifies thyroiditis much earlier in the progression of the disease. All of these assays are relatively inexpensive, and the information they provide in invaluable to establishing a diagnosis.  University Veterinary Medical Colleges such as the U. of Illinois and Michigan State University have state of the art diagnostic instrumentation that have advanced the ability and accuracy of local veterinarians attempts to establish the presence of hypothyroidism in their patients. TREATMENT

L-thyroxine (T4) tablets are generally administered twice a day.  When given twice a day, most veterinarians prescribe 0.1 mg/10 pounds twice per day as the initial dosage.  Repeat exams and occasional follow-up blood testing really helps to fine tune the proper amount of medication needed for each patient.Is hypothyroidism inherited?  Evidence indicates some familial patterns of inheritance.  There are more than half a dozen studies reporting the familial incidence of autoimmune thyroiditis.  Much of the research on hypothyroidism is dogs has been done at Michigan State University  Veterinary School.Not all cases of hypothyroidism are due to autoimmune lymphocytic infiltration of the gland.  There can be other "inducers" of the disease such as consumption of too much Iodine.  These inducers can be very difficult to identify.Humans may acquire what is called Hashimoto's Disease, a genetically transmitted form of hypothyroidism but this disease is not the same as autoimmune thyroiditis in dogs.  In Hashimoto's Disease females are five times more likely to get the disease than males.  There are other differences, as well.CANINE HYPOTHYROIDISM: CASE PRESENTATIONThe following case represents a fairly atypical case of hypothyroidism in that most cases are identified prior to such advanced skin and coat signs.  The dog had been treated for non-specific allergies, and in fact does some allergic problems and skin scarring due to chronic inflammation of the skin.  However, once the Hypothyroidism was discovered and proper treatment instituted, the allergic conditions were less severe simply because the skin became much healthier and more resistant to infections, irritants and allergens.This is how a dog recently looked when presented...  Hypothyroidism was suspected and the blood values of thyroid hormone supported the presumptive diagnosis.   The dog was placed on Soloxine in early June, 2001 and the photos in the second row show the improvement in her after six weeks on medication. You can see what a change can occur when a diagnosis of Hypothyroidism is made and proper therapy instituted. The dog's owners report excellent new growth of hair, renewed vigor and weight loss... all improvements! See blood sample values below:

Hypothyroidism is rare in toy and miniature breeds of dogs. Research definitely indicates that most hypothyroid cases are inherited.  In fact it is fairly common in certain breeds such as...  Golden Retrievers, Doberman pinschers, Greyhounds, Irish Setters, Dachshunds, Cocker Spaniels, Shetland Sheepdog, Boxer, and English Setter .

Thyroid Gland Evaluation:  Blood Test Values In A Dog

Test	Results	Normal Ranges
Total Thyroxine (TT4)	8.0	Normal is 15 to 50
Total Triiodothyronine  (TT3)	0.7	Normal is  1.0 to 2.5
Free (unbound) T4	3.0	Normal is 12 to 33
Free (unbound)  T3	QNS	(Insufficient quantity to test)
T4 Autoantibody	7.0	Normal is less than 20
T3 Autoantibody	3.0	Normal is less than10
TSH (Thyroid Stimulating Hormone)	55	Normal is up to 37mU/L
Thyroglobin Autoantibody	88	Normal is less than 200

 

 

This dog will need to be on thyroid supplementation for life but the medication is not expensive and the patient has resumed a more normal attitude and looks much improved.  Be sure to ask your veterinarian to check for hypothyroidism if your dog displays a poor coat, weight gain, poor exercise tolerance and seeks warm areas in which to spend time.