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CANINE HYPOTHYROIDISM |
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Hypothyroidism in The Dog
What is Hypothyroidism
Hypothyroidism in the dog can be due to a number of issues associated with the production of specific thyroid hormones, with the delivery of those hormones to target tissues, with immune mediated interference with proper chemical structure the hormones and with damage to the thyroid gland itself. Hypothyroidism is the most common endocrine gland disorder in the dog. The endocrine glands are listed below. All of these tissues secrete chemical substances called hormones that have a profound effect on certain "target" tissues. A hormone is a chemical that acts on or with tissues throughout the body and is carried away from the gland of production by the blood stream. Saliva, for example, is secreted by various salivary glands but is not considered a hormone because it leaves the glands via a small duct (a small tube) and is not transported by the blood stream and does not have an effect on any body tissue physiology.
| Thyroid Gland (the Master Gland)
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| Hypothalamus |
Pancreas |
Thymus |
Anterior Pituitary |
Pineal Gland |
| Testis |
Ovary |
Parathyroid Glands |
Posterior Pituitary |
Adrenal Glands |
Of all those glands
and hormones, the thyroid gland is considered the Master Gland.
If the thyroid gland is malfunctioning, every cell in the body is
affected. No wonder dogs, properly diagnosed with hypothyroidism
and placed on appropriate thyroid hormone supplements, will look, act
and feel so much better than before treatment.
SIGNS
Most dogs show signs of hypothyroidism between 3 and 5 years of age but
a diagnosis isn't made in some
dogs
until they are years older. Males and females
seem to be equally affected. Routine testing of young dogs is
not commonly done unless the veterinarian has a reason to suspect
low thyroid function. Some veterinarians believe that if a dog
has not acquired hypothyroidism by 5 or 6 years of age, the odds are
good that it will never be a problem for that individual. (Cats
rarely acquire hypothyroidism but have more trouble with
hyperthyroidism,
especially older cats.)
One of the most commonly seen signs that a dog may have insufficient
secretion of thyroid hormone, or issues with immune mediated thyroid
dysfunction, is weight gain with apparently little food intake.
Any overweight pet should be checked for hypothyroidism. (See
this page for tips on how to get a pet to lose weight.) In
long-standing cases there often is lack of
proper hair coat and even hair loss. This loss generally displays
a pattern over the lumbar area on both sides, sparse hairs on the back
of the rear legs and lack of hair along the abdomen. The coat
tends to lack luster and the finer hairs of the undercoat may be
missing entirely. Most dogs with hypothyroidism lack energy,
prefer warm environments and have poor exercise tolerance. Of great
concern to breeders is the fact that dogs with hypothyroidism may be
infertile and many breeders have their dogs tested for thyroid function
prior to breeding; in dogs with a poor breeding history, hypothyroidism
often is the culprit.
| Hypothyroidism is rare in toy and
miniature breeds of dogs. Research definitely indicates that most hypothyroid cases are inherited. In fact it is fairly common in certain breeds such as... |
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| Golden Retrievers |
Doberman pinschers |
Greyhounds... Caution! Updated info on Greyhounds and their apparent normally low thyroid hormone levels can be viewed here |
| Irish Setters |
Dachshunds |
Cocker Spaniels |
| Shetland Sheepdog |
Boxer |
English Setter |
DIAGNOSIS
If the physical exam or history indicates probable hypothyroidism, the
veterinarian will take a blood sample and have one or more tests run.
The most common tests for thyroid function are T4 (the main Thyroid
hormone) and canine TSH (Thyroid Stimulating
Hormone from the Pituitary Gland). If the screening test using the T4
analysis indicates low a value for T4, further evaluation is very
important in determining the actual origin of the dysfunction causing
the signs of hypothyroidism. Some veterinary laboratories now
recommend TgAA (Thyroglobin Auto-antibody) analysis be done because it
identifies thyroiditis much earlier in the progression of the disease.
All of these assays are relatively inexpensive, and the information
they provide is very important for establishing a
diagnosis. University Veterinary Medical Colleges such as the U.
of Illinois and Michigan State University have state of the art
diagnostic
instrumentation that have advanced the ability and accuracy of local
veterinarians
attempts to establish the presence of hypothyroidism in their patients.
TREATMENT
L-thyroxine (T4) tablets are generally administered twice
a day. When given twice a day, some veterinarians prescribe
0.1 mg/10 pounds twice per day as the initial dosage but each case
is considered individually. Repeat exams and occasional follow-up
blood testing really helps to fine tune the proper amount of medication
needed for each patient.
Is hypothyroidism inherited? Evidence indicates some familial
patterns of inheritance. There are more than half a dozen
studies reporting the familial incidence of autoimmune thyroiditis
where
the dog's immune system actually damages its own thyroid gland.
Much of the research on hypothyroidism is dogs has been done at
Michigan State University Veterinary School.
Not all cases of hypothyroidism are due to autoimmune lymphocytic
infiltration of the gland. There can be other "inducers" of
the disease such as consumption of too much Iodine. These
inducers
can be very difficult to identify. Humans may acquire what is
called Hashimoto's Disease, a genetically transmitted form of
hypothyroidism
but this disease is not the same as autoimmune thyroiditis in
dogs.
In Hashimoto's Disease females are five times more likely to get the
disease than males. There are other differences, as well.
The following case
represents a fairly atypical case of hypothyroidism in that most cases
are identified prior to such advanced skin and coat signs. The
dog had been treated for non-specific allergies, and in fact does some
allergic problems
and skin scarring due to chronic inflammation of the skin.
However, once the Hypothyroidism was discovered and proper treatment
instituted, the allergic conditions were less severe simply because the
skin became much healthier and more resistant to infections, irritants
and allergens.
This is how a dog recently looked when presented...
Hypothyroidism was suspected and the blood values of thyroid hormone
supported the presumptive diagnosis. The dog was placed
on Soloxine in early June, 2001 and the photos in the second row show
the improvement in her after six weeks on medication. You can see what
a change can occur when a diagnosis of Hypothyroidism is made and
proper
therapy instituted. The dog's owners report excellent new growth of
hair,
renewed vigor and weight loss... all improvements!
| Test |
Results |
Normal Ranges |
| Total Thyroxine (TT4) |
8.0 |
Normal is 15 to 50 |
| Total Triiodothyronine (TT3) |
0.7 |
Normal is 1.0 to 2.5 |
| Free (unbound) T4 |
3.0 |
Normal is 12 to 33 |
| Free (unbound) T3 |
QNS |
(Insufficient quantity to test) |
| T4 Autoantibody |
7.0 |
Normal is less than 20 |
| T3 Autoantibody |
3.0 |
Normal is less than10 |
| TSH (Thyroid Stimulating Hormone) |
55 |
Normal is up to 37mU/L |
| Thyroglobin Autoantibody |
88 |
Normal is less than 200 |
| Click on the image to see a
close-up view. |
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| Above... Before
Treatment
Below... After Treatment Click to enlarge the photos |
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click to
enlarge photos |
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This dog will need to be
on thyroid
supplementation for life but the medication is not expensive and the
patient
has resumed a more normal attitude and looks much improved. Be
sure
to ask your veterinarian to check for hypothyroidism if your dog
displays
a poor coat, weight gain, poor exercise tolerance and seeks warm areas
in
which to spend time.
(See this page
for tips on how to get a pet to lose weight.)
The study of
Greyhounds and Thyroid Testing has been competed and the results
reported in an article written by Dr. Marcus Rick and published in the
GCA Fall 2005 Newsletter. Of one hundred samples that were
collected, 98 were analyzed statistically to establish a reference
range of thyroid test results in the Greyhound. The majority of
the samples were from AKC registered Greyhounds, seven were from NGA
dogs. The results were then compared graphically with the
reference range for the general dog population used at Michigan State
University and the result ranges from three previous studies by other
researchers.
Dr. Rick states “Overall it can be seen that the reference range of
Greyhounds is considerably less than that of the general canine
reference range.” In very short summary he concludes:
1.) Overall, hypothyroidism is very unlikely in the
Greyhound, however well documented cases exist.
2.) If either total T4 of free T4 by dialysis are detectable with
the currently available assays (GT 6nmol/L, GT 2pmol/L, respectively)
it is very likely that your Greyhound is NOT hypothyroid.
3.) Lymphocytic thyroiditis is unlikely as well. Of 1,409
Greyhound samples received at Michigan State University, 2 % were TgAA
positive compared with 10 % of 143,800 dogs of the general dog
population. Of these 1,409, only 43 (3%) had thyroid results
including elevated TSH consistent with hypothyroidism compared to 8 %
of
the general 143,800 samples.
4.) Diagnosing hypothyroidism might be difficult due to decreased
reference values that, in many cases, are below the detection limit of
currently available assays.
5.) Greyhound-specific complaints, including bald thigh syndrome,
poor racing performance, and infertility do not have an
association to thyroid hormone concentrations. Supplementing
these animals with thyroxine is not recommended.
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What is hypothyroidism?http://www.upei.ca/ciddrelated terms: familial thyroiditis, lymphocytic thyroiditis, congenital hypothyroid dwarfism |