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  Hypothyroidism

 

Common names or abbreviations:

bulletThyroid Dysfunction, Hypothyroidism, Thyroiditis, Hashimoto's Disease

Description or definition:

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Canine hypothyroidism is the absence of sufficient thyroid hormone to maintain healthy body functions.  The term hypothyroidism has been loosely applied to describe all stages of this disease process whereas strictly speaking it should be reserved for the end-stages when the animal's thyroid gland is no longer capable of producing sufficient hormone(s) to sustain clinical health. At this point, the dog can express any number of the non-specific multisystem signs of thyroid dysfunction.  The age of onset is usually between one and six years of age.  Cases have been reported in Golden Retriever, Great Dane, Beagle, Borzoi, Shetland sheepdog, American Cocker Spaniel, Labrador retriever, Rottweiler, Boxer, Doberman pinscher, German shepherd, Akita, Old English sheepdog, and Irish setter.  The incidence of autoimmune thyroiditis in males and females is similar, so it is equally important to test both prior to breeding.

The most common cause of canine thyroid disease is autoimmune thyroiditis (estimated 90% of cases). Thyroiditis is an immune-mediated process that develops in genetically susceptible individuals and is characterized by the presence of antithyroid antibodies in the blood or tissues. Thyroiditis is believed to start in most cases around puberty, and gradually progress through mid-life and old age to become clinically expressed hypothyroidism once thyroid glandular reserve has been depleted. During this process, the animal or person becomes more susceptible to immune-mediated or other diseases affecting various target tissues and organs. The prerequisite genetic basis for susceptibility to this disorder has been in established in humans, dogs and several other species.

 

About half of canine hypothyroidism has been reported to be associated with autoimmune thyroiditis (positive TgAA- Thyroglobulin Autoantibody); the majority of the remaining hypothyroidism is idiopathic (without apparent cause and TgAA negative), while a small fraction is from a pituitary disorder.  A number of scientific publications have presented data to support the genetic transmission of autoimmune thyroiditis, others have reported the familial (occurring among relatives) incidence of the disease and still others report cases from surgical removal of the gland, cancer, low iodine in the diet and many other causes.

 

Symptoms

 

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Typical clinical signs can mimic other diseases like Degenerative Myelopathy and include weight gain, skin abnormalities, weakness, unprovoked aggression towards other animals and/or people, sudden onset of a seizure disorder in adulthood, disorientation, moodiness, erratic temperament, periods of hyperactivity, hypo-attentiveness, depression, fearfulness and phobias, anxiety, submissiveness, passivity, compulsiveness and irritability.  After the episodes, a majority of the animals were noted to behave as if they were coming out of a trance-like state and were unaware of their previous behavior.

 

Diagnosis:

 

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The latest tests include measurement of two forms of the thyroid hormones T3 (triiodothyronine) and T4 (levothyroxine) and a search for antibodies that could indicate autoimmune thyroiditis, the genetic form of the disease. Interpretation of the numbers recorded is as important as the numbers themselves, for the relationship between the hormones is complex. In addition, normal ranges of hormone vary somewhat with the breed or mix.

The best current marker for this disease is a positive TgAA (Thyroglobulin Autoantibody) test result.  Assuming a single gene disorder and recessive trait, TgAA will be positive only in dogs having both genes for thyroiditis.  The Orthopedic Foundation for Animals (OFA)3 started a Canine Thyroid Registry and has certified a number of regional veterinary laboratories in the US and Canada qualified to perform the thyroid profile for registry purposes. Oxford Laboratories4 began producing a commercially available assay for TgAA so all reagents for the OFA profiles are standard among certified laboratories.

 

For further information on the Canine Thyroid Registry, contact the OFA:  Telephone: 1-573-442-0418.

Treatment:

 

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Treatment consists of two daily doses of levothyroxine, the hormone identified in the test as T4.  Levothyroxine is converted to triiodothyronine by the body; dogs that cannot make this conversion will need both levothyroxine and triiodothyronine.  The dosage is based on body weight; thyroid hormones are quickly metabolized and excreted from the body, so splitting the dose is most effective.  The initial improvements are usually seen during the first week of therapy (an increased mental alertness, greater activity, more muscle strength, and improved appetite).  The improvements in the skin and hair take a bit longer (several months) to return to normal.  One to two months after starting the dog on therapy, the veterinarian will redo the tests to make sure the levels are within the normal range.  Blood should be drawn four-to-six hours after the morning dose.  Dogs on long-term therapy should have a complete panel of tests every six to 12 months.

 

 Prevention:

 

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There is no DNA based testing procedure at this time, testing with the best available marker, TgAA, can be beneficial. Selective breeding should reduce the prevalence in high incidence breeds and prevent an increasing prevalence in low incidence breeds. Although males were similar to females in prevalence, you can imagine the impact one important but affected male could have on the breed, especially a breed with small numbers. The TgAA portion of the thyroid profile is most important during the first 5 years of life as few dogs are found to have idiopathic hypothyroidism before this age.

While there is a genetic predisposition for thyroid disorders, environmental factors such as pollutants and allergies probably play a role as well.

Links to sites about this disease:

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http://www.americanboxerclub.org/health/boxerhypothyroidism.htm

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http://www.canine-epilepsy-guardian-angels.com/ThyroidDisease.htm  (Clinical Signs)

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http://www.canismajor.com/dog/thyroid.html

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http://www.borzoihealth.com/documents/hypothyroidism.pdf

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http://www.uskbtc.com/article.php/90

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http://www.vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00158.htm

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http://www.atlanticstates.org/thyroid.htm

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http://thyroid.about.com/cs/catsdogspets/a/hypothyroiddogs.htm

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http://www.thyroid-info.com/articles/dog-hypo.htm

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http://www.goldens.com/tip8.html

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http://www.cslabs.co.uk/canine%20thyroid%20page.htm (Veterinary Handbook)

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http://www.tmcamerica.org/TMCA/Sentinel4/hypothyroidism.htm

 

 

 

Dedicated to improving the health of ISSR Shiloh Shepherds.

 


Copyright © 1998 - 2009. Shiloh Shepherd Dog™ Club of America.
All rights reserved. Revised: January 2008

The information on this website was written by ISSR breeders and other concerned individuals, however we are are NOT veterinarians. This information is being provided as a general overview, from information we were able to find about each disease through our own research. These summaries are not intended to be relied upon as medical or veterinary advice, nor do we consider ourselves experts in the veterinary field or in any of these conditions. While we do our best to provide the most up to date information, new research is constantly being done on these diseases. We recommend that you do further study and talk to your veterinarian on any topics you see here, as we cannot guarantee that the information posted here is the most current information available.  This site was originally designed and maintained by Debbie Knatz.