The thyroid is considered a "master gland" as it is involved in so many metabolic processes in our dogs. While it may not be obvious when things are going well, if your dog becomes hypo or low thyroid, you can see a number of clinical signs.
Some of the first signs many people notice are problems with the haircoat. Hypothyroid dogs will often have a thin, brittle coat. They may lose undercoat and not replace it quickly or at all. Some dogs will even have symmetrical areas on the body that have very little hair. These dogs will have a low tolerance for cold weather unlike the normal Terv who loves to romp in the snow.
Other signs can be more serious. Hypothyroidism can cause muscle weakness and nerve damage. A stiff gait, jumping problems in agility dogs, and laryngeal paralysis have all been associated with hypothyroidism. Difficulty swallowing and megaesophagus with the development of aspiration pneumonia also can be side effects of a low thyroid level.
Changes in behavior including hyperactivity and aggressive behaviors may be connected to low thyroid levels. Or, lethargy and mental dullness may be noted. For a breeder, infertility is a sad side effect. Both male and female dogs are affected with bitches having short heats and males exhibiting testicular atrophy.
The greatest cause of hypothyroidism is autoimmune thyroiditis, meaning your Terv’s own body attacks its thyroid gland. You may also see this called lymphocytic thyroiditis. There is also idiopathically low thyroid – meaning we don’t know why the level is low.
So how can we avoid hypothyroidism and catch it early in dogs who have it before they have any serious side effects? Blood work is the key here. Some of you may remember doing TSH (thyroid stimulating hormone) response tests. You drew blood for a baseline thyroid level, then gave TSH and drew a second sample to see if the thyroid responded to stimulation. This test basically gave you the T4 (tetraiodothyronine) level of your dog. Those days are long gone.
We still do blood work but newer tests have helped to refine the diagnosis. Currently a blood sample is drawn and up to eight parameters are evaluated. These include: TT4 (total thyroxine), TT3 (total tri-iodothyronine), FT4 (free thyroxine – not bound to any proteins in the blood), FT3 (free tri-iodothyronine), T4AA (autoantibodies to T4), T3AA (autoantibodies to T3), TSH (canine thyrotropin or thyroid stimulating hormone) and TgAA (thyroglobulin autoantibodies).
OFA (Orthopedic Foundation for Animals) looks at three values to make their assessment of your dog. The FT4 by the dialysis method, the TSH level and the presence or absence of TgAA are the tests they use. Michigan State prefers to do the eight parameters mentioned above for their rankings and recommendations on care.
The three antibody tests – TgAA, T4AA and T3AA indicate that your Terv has an immune problem with his thyroid. If your dog tests positive for TgAA, then OFA considers your dog to have autoimmune thyroiditis. High levels of TSH are also indicative of a thyroid gland in trouble.
Ideally your Terv will have normal levels of FT4 by dialysis, normal levels of TSH and no TgAA. Some dogs will have a low level of free T4 by dialysis from outside influences. This could include a severe illness of some sort or medications such as glucocorticoids, phenobarbital and phenylbutazone. Sulfa type antibiotics can also lower thyroid levels as well as an iodine deficient diet. These dogs should be retested. Vaccinations have not been shown to influence thyroid levels according to MSU but estrus in a bitch may give a slightly higher than normal value.
Belgian Tervurens should have thyroid levels checked yearly from about 2 to 6 years of age, then every other year or so. Obviously if you notice any clinical signs you should check right away. OFA will only issue certification on dogs over a year of age and they recommend rechecks. They currently have a list of eight laboratories approved to run the OFA thyroid panel.
OFA Data: Belgian Tervurens #47th of all breeds listed with 292 dogs tested. Of these Tervs, 78.4% tested normal. 2.1% were diagnosed with autoimmune thyroiditis, 0.3 % had idiopathic hypothyroid function and 19.2% were listed as equivocal. Any dog that does not have normal FT4 by dialysis, normal TSH and no TgAA will be listed as thyroiditis or equivocal. Clearly Tervs have a number of clinically normal dogs with at least one blood value out of whack. Also, a dog may test normal at one or two years of age, but show thyroiditis at 5 years of age. This is why rechecks are so important.
Michigan State University (MSU) data: Belgian Tervurens rank 110th of all breeds listed with 632 dogs tested. 3.0% were classified as autoimmune thyroiditis and 4.3% as equivocal.
Clearly thyroid problems do exist in our breed. It is important for any breeder of Belgian Tervuren to do thyroid testing and to do periodic rechecks. If a dog tests positive for hypothyroidism, the dog can be fairly inexpensively treated with thyroid replacement. However, that does not mean that this dog should be treated and then bred. If so, we will perpetuate this problem in our breed and perhaps make it much worse.
Recommended websites: www.offa.org and www.animalhealth.msu.edu/documentsFAQThryoidFunctioninDogs
Deb M. Eldredge, DVM
For ABTC August 2006
EVALUATING THE THYROID
The thyroid gland is rightfully considered a "master gland" due to its multiple effects throughout the body. In dogs, the most common problem is hypo or low thyroid levels. Clinical signs can vary a great deal in individual dogs, but could include skin problems, obesity, lethargy and even lameness. Thyroid levels can appear to be low when a dog has a normal thyroid but is currently ill from something else as well.
More and more breeders of purebred dogs are screening their breeding stock for thyroid problems. OFA (Orthopedic Foundation for Animals) is starting to certify thyroid levels for dogs and Michigan State University has long had the lead in testing for and maintaining thyroid level evaluations. The question has arisen with the onslaught of new tests as to which values are the most relevant and which tests best reflect that.
There are three basic values to check out - thyroxin (T4, both free and total), triiodothyronine (T3) and thyroid stimulating hormone (TSH). These are all tests done on a blood sample. There are also autoantibodies to these, but these are the basic three. The original "gold standard" test for thyroid problems in dogs involved the use of TSH to stimulate the thyroid and then evaluate the response. Unfortunately TSH is quite expensive and currently not available in the United States.
In humans, hypothyroidism has been diagnosed primarily by the level of free T4 and the amount of TSH. It is just recently that a test has been developed to measure the concentration of canine TSH and it was hoped that this would be a major diagnostic breakthrough. An article in the Journal of the American Veterinary Medical Association in the December1, 1997, Vol. 211, No 11 discusses the various tests used and their efficacy. "Measurement of serum total thyroxin, triiodithyronine, free thyroxin and thyrotropin concentrations for diagnosis of hypothyroidism in dogs" by Mark Peterson DVM, Carlos Melian DVM and Rhett Nichols, DVM compares the various values commonly detected to see which best indicate true hypothyroidism.
Most dogs have primary hypothyroidism (low production and/or secretion of thyroid hormones) so we would expect low levels of total and free thyroxin with high levels of TSH (trying to stimulate more production). In dogs with clinical signs, a decreased level of T4 was considered to be about 90% sensitive. This means most hypothyroid dogs have a low level of T4. Specifically checking free T4 made this diagnosis even more accurate. As mentioned above, severe nonthyroid illness can cause a decrease in T4 also, so you do want to correlate clinical signs with the results. The ideal method for measuring free T4 was felt to be the dialysis method which is just recently developed.
Measuring T3 levels was not helpful in this study in differentiating between normal (euthyroid) and hypothyroid dogs. That includes the measurement of T3 autoantibodies, since 40% of the dogs with T3 autoantibodies were normal.
The measurement of TSH alone was also not especially helpful in predicting which dogs were truly hypothyroid. Up to 15% of normal dogs in various studies have been found to have what were considered elevated levels of TSH. Also, 24% of hypothyroid dogs had normal, not elevated, TSH levels.
The conclusion was that the best blood tests to evaluate the thyroid gland in dogs were the T4 level (particularly free T4) in combination with the TSH level. Having a low T4 concentration and an elevated TSH level were the best indicators of a true hypothyroid dog.
I think this shows us what tests we want to be sure are included in a thyroid profile on our dogs and helps us to interpret the test results. Remember that thyroid tests should be done on dogs at least 2 years old and probably repeated every 2 to 3 year since thyroid problems often develop as the dog ages. I hope this helps you somewhat as we all wade through the explosion of information now available about the thyroid gland and the tests used for diagnosis.
Deb Eldredge, DVM
Feb 1998 for Kuvasz Times
Reprinted by permission.