Hypothyroidism - is it on the rise? In a 1995 survey it was found that thyroid disease is the number one health concern of major breed clubs. It seems to have increased in frequency in cogs, but has it really? 15-20 years ago, breeders weren't testing dogs with the frequency that they are today, so there's no way of telling whether the incidence of hypothyroidism was higher, lower or the same 20 years ago.
OVER DIAGNOSED OR UNDER DIAGNOSED?
Is hypothyroidism being over-diagnosed? Adding to the increase in statistics are dogs being treated for hypothyroidism based on low T3 and T4 levels alone, which isn't a good indication of hypothyroidism. So many other things can give false low T3 and T4 levels: such as the time of day, physical condition of the dog, concurrent medication, and concurrent illness. It's become apparent that many owners are asking their Vets to prescribe synthetic thyroxin for dogs coming back in the low normal range, because of vague symptoms that could easily be attributed to various transient problems, viruses, bacteria, or poor nutrition. It was also common to give unnecessary thyroid medications to show dogs to get a better coat for the show ring. After being supplemented for a long time, the system tends to compensate, and if the supplement is removed, the dog is hypothyroid for about 30 days.
The fact is that we don't know the exact "normal" thyroid level for each breed. Different breeds have different "normal" thyroid levels. If the dog shows no symptoms of being clinically hypothyroid, should we test for it? If the dog is asymptomatic, it probably has the correct level for that individual dog. That's the "if it ain't broke, don't fix it theory." The University of Tennessee is involved in a project to develop a thyroid test for use exclusively in canines. Apparently the existing tests were all developed for use in people and then adapted to canines.
There's a different type of test other than simple serum T3 and T4, that can give you a more accurate idea if autoimmune thyroiditis is involved. More about that later in the "when to test, and what to test" section of this article.
GENETIC OR CAUSED
Because of the amazing number of breeds that have developed this "hereditary" problem, many scientists are beginning to look for a man-made cause to this problem. Evidence is pointing towards the possibility of common environmental toxins, vaccine overload, and the diet being fed to today's dogs being the causative agent of hypothyroidism. All of these theories need further investigation, but are interesting possibilities. Let's look at a few of them.
Many of today's pesticides mimic the structure of mammalian hormones. Further, chicken, and beef are often laced with steroids and antibiotics on purpose to increase mass for market. It is reasonable to hypothesize that some canine endocrine problems may be caused by these additives.
On May 1, 1997 there was a consensus statement issued by 18 scientists about toxic chemicals and the immune system. The meeting was initiated because of the pervasive contamination of the environment by compounds having the potential to disturb the immune system of mammals. Certain synthetic chemicals can cause alterations of the immune system. Alterations in immunologic function can translate into altered host resistance and susceptibility to disease, including autoimmune disease. This area is in need of more research, but the widespread exposure of populations of humans and other mammals has made it difficult, of not impossible to find control populations that have no exposure level. In other words, we are all now exposed to many chemicals that can change our immune system, so it is not possible to find a control group of mammals who have truly healthy unaffected immune systems that can be studied.
Other causative agents being considered are serum overload from combination vaccines, immune-suppressant viruses, ethoxyquin, and the fat source used in dried kibble.
Viruses of the retrovirus and parvovirus classes have been recently implicated as the cause of autoimmune endocrine disorders, especially of the thyroid gland (Thyroiditis), adrenal gland (Addison's disease), and pancreas (Diabetes). Viral disease and recent vaccination with single or combination modified live-virus vaccines, especially those containing distemper, adenovirus 1 or 2, and parvo virus are increasingly recognized contributors to immune-mediated blood disease, bone marrow failure, and organ dysfunction.
The Fat source in dried kibble - is almost always polyunsaturates today, instead of saturated fats needed to absorb Vitamins A, D, E & K. Vitamin A deficiencies leave the body vulnerable to a slowdown in growth and repair of body tissues, skin disease and susceptibility to mucus membrane infections of the mouth, nose, throat, and lungs. Fighting off the effects of air, water and environmental pollution may be hampered, as well as protection of soft tissue and all linings of the digestive tract, kidneys, and bladder. Proper secretion of gastric juices necessary for digestion may be impaired. In animal studies, researchers believe vitamin A fights off cancerous attacks by activating the body's immune system and preventing the thyroid gland from shrinking. So, if a lock of soluble fat in our canine diets may be causing a vitamin A deficiency, a multi-organ disease pathology or increasing prevalence of thyroid dysfunction may be worthy of consideration.
Ethoxyquin - A Tufts study indicated that the synthetic antioxidant ethoxyquin reduced the blood plasma level by 42%. Further study showed that this interfered with the utilization of selenium. This is where the immune system is affected. Starting with a Welsh study that demonstrated that rats fed a diet deficient in E and selenium produced pups that were born immune compromised.
DEFINITIVE PROOF?
Is their definitive proof that it is a manmade condition? The answer is no. Even if you did breeding studies in which offspring are raised under similar conditions, or from studies in which litters are divided and the sub-sets given different vaccine regimens, different foods, etc. the relationships would be extremely difficult to unravel statistically from observational or survey data. Was it caused by the poor diet or the serum overload from the vaccines, or was the dog carrying the gene, while his brother who was fed the good diet and was not challenged by vaccine overload was not carrying the gene. This type of research may be advanced with the use of cloned animals, which would be identical physically and genetically!
THE THYROID
A little about the thyroid. This small gland is a hormone producer that affects many parts of the body. There are 2 forms of thyroid hormone secreted by the thyroid gland: T3 (triiodothyronine) and T4 (thyroxine). T3 is usable thyroid hormone, while T4 must first pass through the liver and other tissues before it can become T3, the usable thyroid. The thyroid gland itself is regulated by two different hormones. TRH (thyroid releasing hormone) and TSH (thyroid stimulating hormone). When the brain senses that T4 is low the TRH will first be released into active duty, followed by the TSH. Hypothyroidism, the shortage of usable thyroid in the body is usually the condition seen when a thyroid imbalance is suspected. Hyperthyroidism is uncommon in dogs.
What are the symptoms of hypothyroidism? There are many: some vague, and some very noticeable. We'll name a few here, as space permits.
Why do skin problems seem to go hand and hand with thyroid imbalance? In order for dogs to have healthy skin and coats, the cells that make up the body must be healthy and multiply. It is not fully understood, but the thyroid gland is essential in regulating the metabolism of each individual cell. Whenever cells cannot function efficiently, once of the visible results is the skin will loose it's elasticity, and can ultimately result in dry, crusty, scaly skin. The end result is a dog with a sparse coat, and a dull hardened gray skin that will have an obnoxious odor. A dog left untreated will be miserable with uncontrollable itching all over.
WHEN TO TEST & WHAT TO TEST
When to test: A thyroid panel should be done in the middle of a bitch's cycle, as being near the heat cycle can effect the results.
What to test: Since the T3 and T4 alone, aren't good indications of thyroid disease, what should you be testing for?
You'll want to get a Total T3 and T4, plus Free T4 by equilibrium dialysis, Free T3, endogenous TSH (thyroid stimulating hormone) and TgAA (Thyroglobulin Autoantibodies)
Most cases of thyroid disease start out as autoimmune thyroiditis. This being the case there will be anti-thyroid antibodies in the blood. If the test comes back positive for anti-thyroid antibodies, you'll have a definitive diagnosis of hypothyroidism, even before clinical symptoms appear.
The Orthopedic Foundation for Animals (OFA) now has a canine thyroid registry. The following approved laboratories currently can accept samples. Contact them for appropriate submission forms, sample handling procedures, and laboratory service fees, before collecting the specimen.
Animal Health Diagnostic Laboratory
Endocrine Diagnostic Section
P.O. Box 30078
Lansing, MI 48909
(517) 353-0621
Diagnostic Laboratory
New York State College of Veterinary Medicine
Cornell University, Upper Tower Road
Ithaca, NY 14851
THOUGHTS
While it's common sense to avoid the unnecessary overuse of antibiotics, pesticides and vaccines; to totally eliminate them would be impossible and unwise. Used carefully, they contribute to the quality of life. Think of the numbers of human and canines that would have perished without them. Medicine and technology are part of our life, and part of our future. The idea that combinations vaccination schedules as they are now implemented "produce" autoimmune disorders needs more investigation. It's far from being proven. Secondly, since some breeds seem more prone to developing "overchallenge" type disorders, could that not indicate a genetic predisposition? Some autoimmune disorders are gene-based. Some are not. Until a way to distinguish one from the other comes to pass, we won't have any way of knowing if an animal is affected by one or the other, or both. Therefore when presented with evidence of autoimmune hypothyroidism you need to weigh carefully the risks of breeding that animal and passing on the possibility of a predisposition to her/his get.
90% of this article was researched on the Internet. From articles available on genetics, & biology, from conversations with geneticists, environmental scientists and biologists via e-mail, and from postings from canine genetics lists. The Internet is not just for silly chat rooms and entertaining games; it can be a great educational resource!
