by: Internal Article

Dogs with hypothyroidism have impaired production and secretion of thyroid hormones resulting in a decreased metabolic rate.  The disorder may be acquired (a progressive deficiency of thyroid hormone) or congenital (present at birth).  The acquired form is the most common in dogs and appears to be widespread in Alaskan malamutes, though we need more data to determine its exact prevalence.

Found most commonly in dogs aged four years or older, the disorder is the result of gradual atrophy of the thyroid gland or progressive replacement of the thyroid gland with lymphocytes due to an autoimmune process (lymphocytic thyroiditis).  The disease tends to run in families and is therefore thought to be genetic, though the exact mode of inheritance is unknown.  Affected dogs should not be bred.

A broad range of clinical signs make hypothyroidism a challenge to diagnose. Early signs include lower energy levels, unusual episodes of aggression, and increased susceptibility to infections.  As the disease progresses, the dog may develop symmetrical hair loss, darkening of the skin, or dry or greasy hair.  Other clinical signs include a slow heart rate, lethargy, difficulty maintaining body temperature, mental dullness, exercise intolerance, infertility, constipation and weight gain.  A dog may exhibit all or only a few of these symptoms.  When hypothyroidism is suspected, ask the veterinarian to do a complete thyroid assay.

Standard treatment consists of thyroxin supplementation once or twice a day for life.  Within a week of starting treatment, the dog's attitude and activity levels should improve, although improvement in the skin and coat can take up to six weeks or more.  With treatment, all symptoms should eventually disappear.  If they do not, consider whether your dog may have been misdiagnosed.  Because the symptoms are similar to those present in a variety of other disorders, hypothyroidism is among the most overdiagnosed of canine diseases.


Developed from information contained on the 1998 Canine Inherited Disorders Database Web site and from Merck Veterinary Manual.

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Offsite References

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 Canine Hypothyroidism - Borzoi Club of America Health Committee Website
The Borzoi Club of America health committee website provides the summary of the Michigan State University study and includes some information breeders need to know.
  Canine Hypothyroidism - Newman Veterinary Medical Services
There are a few different types of hypothyroidism, and this link gives an overview of each.  Among the topics are: lymphocytic hypothyroidism, idiopathic hypothyroidism, primary, secondary, and tertiary plus links to info on diseases which may look like hypothyroidism.  This site also provides pictures of dogs with symptoms.  This is one of the better websites for explaining hypothyroidism. 
 Canine Thyroid Disease - Epi Guardian Angels
article from Antech News, November 1998, detailing the diagnosis and treatment of this common canine affliction
  Disorders of the Thyroid Gland
(Word Document)

by Thomas K. Graves, DVM, PhD, DACVIM
Briefly touches on primary vs secondary hypothyroidism. 
Comments on Thyroid Disease - Epi Guardian Angels
Seizures can be caused by hypothyroidism, though the exact connection is unclear.  WB Thomas DVM, Dipl.ACVIM and W. Jean Dodds, DVM explain the possible connection.
  Effects of Moderate to Severe Osteoarthritis on Canine Thyroid Function - 
The Canadian Veterinary Journal

Although entirely hypothetical, it is plausible that chronic pain due to moderate to severe chronic osteoarthritis could induce sufficient stress to alter thyroid function.
Vaccines Stop Disease; Risks Remain - DVM Newsmagazine
by Marilyn E. Stiff, MA, DVM, Dipl. ACVIM
This article briefly touches on the difference between idiopathic and lymphocytic thyroiditis, or chronic atrophic autoimmune thyroid disease, and raises questions about the effect of vaccines on the thyroid.
  Hypothyroidism - Provet Healthcare Information
In some cases, TRH is not being produced by the pituitary gland and not enough thyroid stimulating hormone is made for adequate thyroid function.  It is currently unclear as to whether this occurs in dogs.  For information on the several causes of the problem and list of diseases that may cause a low T4, visit this link.
Thyroid - Orthopedic Foundation for Animals
General overview of the disease, and detailed information about the OFA's testing procedures and certification criteria.  Includes breed database.
  Exercise Physiology Canine Publications - Ohio State University College of Veterinary Medicine
Online articles/studies of thyroid and the racing sled dog.


Please check our "Links" page for some personal web sites pertaining to this subject, and stories of affected dogs and their owners.