One of the most commonly seen endocrine disorders in dogs is thyroid dysfunction.  Deficiency of the thyroid hormone is commonly referred to as “hypothyroidism.”  There are two primary forms of hypothyroidism; one being lymphocytic thyroiditis and the other being atrophic hypothyroidism.  The secondary forms of the disorder are pituitary-dependent hypothyroidism and euthyroid sick syndrome. 

            Lymphocytic thyroiditis is an immune-mediated disorder.  Lymphocytes infiltrate the thyroid gland.  It is the most common cause of hypothyroidism and can be a result of your dog’s system reacting to medications, vaccinations, viral infections or heavy metal toxicity from either water or its food supply.  This autoimmune response has been linked to genetics.  Its primary indicator on the thyroid panel is an elevation of the “T3” and/or “T4” auto-antibodies.

Atrophic hypothyroidism comes about when the thyroid gland atrophies.  Thereafter the glandular tissue is replaced with fat.  Cause is unknown.

Pituitary-dependent hypothyroidism results from the insufficient secretion of TSH by the pituitary gland.  This can be caused by drug reactions, illness and/or malnutrition and is usually temporary.  Permanent deficiencies may be caused by tumors, congenital malformation, infections or hemorrhage involving the pituitary gland.  Low levels of TSH on the function test, along with low resting levels of TT4, and FT4 that correct on the TSH stimulation test is the diagnostic test for this type of hypothyroidism.

Euthyroid sick syndrome is trickier to diagnose.  The TT4 and FT4 will sometimes decrease in many severe or chronic illnesses in order to compensate for essential body tissue when there is a decreased caloric intake.  Kidney failure, diabetes mellitus and Cushing’s Disease may cause a decreased secretion of TSH and give a “false” indication that your dog has hypothyroidism. 

The clinical symptoms may involve many body “systems.”  A dog may show many signs of being hypothyroid or only a few.  Signs usually become evident around 4 to 6 years of age; however, giant breeds may exhibit those signs as early as 2 to 3 years of age.  Dogs can be hypothyroid for six months up to a year before the obvious clinical signs become evident to the owner.  However with that said, new studies show that if your dog suddenly exhibits aggressive behaviors, he or she may be hypothyroid and a test may be in order! 

The clinical (text book) signs associated with hypothyroidism are:

In addition to the general “clinical signs” your dog may have, there are many other system-related signs.  Some of these are:








  Blood Disorders

Behavior Disorders

  Other Disorders

  The blood chemistry and CBC of a hypothyroid dog will show: 

If your dog has Lymphocytic hypothyroidism:

  TT4 will be normal to low

FT4 will be normal to low

TSH will be normal to high

TSH Response will be poor

Auto-antibodies will be increased

  If your dog has Atrophic hypothyroidism:

  TT4 will be low

FT4 will be low

TSH will be high

TSH Response will be poor

Auto-antibodies will be normal

  If your dog has Pituitary Dependent hypothyroidism:

  TT4 will be low

FT4 will be low

TSH will be low

TSH Response will be normal

Auto-antibodies will be normal

If you dog has Euthyroid Sick Syndrome:

TT4 will be low

FT4 will be low

TSH will be low

TSH Response will be normal

Auto-antibodies will be normal

Now for the GOOD news!  Treatment of hypothyroidism is very successful!  There are several medications available.  Soloxine is one of the more common drug therapies.  Dosages are usually given twice daily but over time, may be able to be reduced to once daily.  This is, of course, dependent on thyroid response profiles which are usually done at 10 week intervals until the TT4 and FT4 levels are stable (mid-range levels).  Thereafter, yearly profiles are recommended.  Blood drawn four to six hours after dosage will give the most accurate results.  Acupuncture has also been reported to have a beneficial effect for the treatment of hypothyroidism.  However, always consult your veterinarian before commencing any type of drug or treatment therapy.  I am not a vet nor do I portray one on television!  J


Until next time….as author Gene Hill so eloquently wrote:  “No one can fully understand the meaning of love unless he's owned a dog. A dog can show you more honest affection with a flick of his tail than a man can gather through a lifetime of handshakes.”

As always, I can be reached at GoodHeart@telstar-online.net

Reference:  Merck Veterinary Manual; Holistic Guide for a Healthy Dog, 2nd Edition (Volhard & Brown)  

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