In hypothyroidism, the thyroid gland is underactive, and unable to secrete
enough thyroid hormone. This, in turn, decreases your dog’s metabolism.
Hypothyroidism is commonly caused by an auto-immune response; that is,
the body creates antibodies directed against the thyroid glands causing
their destruction. This self-destruction is referred to as autoimmune
thyroiditis or lymphocytic thyroiditis. As this disease
develops, antibodies recognize the thyroid tissue as being foreign, and
lymphocytes - a form of white blood cell - are signaled to cause the actual
destruction. This condition rarely occurs in cats.
In hyperthyroidism, the thyroid gland is overractive, and secretes more
than enough thyroid hormone. This, in turn, increases your cat’s
metabolism. This condition does occur in dogs, but not nearly as often
as hypothyroidism, and certainly not as commonly as in cats. Please refer
to All Our Pets article
on Feline Hyperthyroidism for symptoms and treatments for this disease.
Therefore, the remainder of this article focuses on Canine Hypothyroidism.
What are the symptoms of hypothyroidism?
- Lethargic behavior such as a lack of interest in play, frequent napping,
tiring out on long walks
- Weight gain, sometimes without an apparent gain in appetite
- Bacterial infections of the skin
- Dry skin
- Hair loss, especially on the trunk or tail (“rat’s tail”)
- Discoloration or thickening of the skin where hair loss has occurred
- Cold intolerance/seeking out warm places to lie down
- Slow heart rate
- Chronic ear infections
- Severe behavioral changes such as unprovoked aggression, head tilt,
seizures, anxiety and/or compulsivity
Are there certain breeds that are more susceptible to hypothyroidism?
Many breeds are affected by this disease, including (but not limited
- Golden retrievers
- Doberman pinschers
- Irish setters
- Cocker spaniels
- Airedale terriers
- Hypothyroidism is rare in toy and miniature breeds of dogs.
How is hypothyroidism diagnosed?
All diagnosis begins with an examination and taking of a history. Your
veterinarian will be looking for clinical signs of hypothyroidism during
a thorough physical examination of the dog, and will ask questions about
your dog’s health and behavior. If hypothyroidism is suspected,
a blood test will be ordered. While there are many different tests the
first and principal one is for T4. Dr. Shawn Messonnier in Natural
Health Bible for Dogs and Cats states that this disease
is so common in middle-aged to older dogs that any dog exhibiting chronic
itchy skin and irritations should be tested for its level of T4 - a very
simple and inexpensive blood test. Many dogs go through expensive allergy
tests when the cause of allergy-like symptoms is as simple as hypothyroidism.
How is hypothyroidism treated?
Hypothyroidism is treated with a daily dose of synthetic thyroid hormone
called thyroxine (levothyroxine). Blood samples will need to be drawn
periodically to assess the effectiveness of the dosage and make any adjustments
What should I expect from the treatment?
Most symptoms should clear up after treatment. With regularly scheduled
check-ups to ensure correct dosage, your dog should be mostly symptom-free
for the rest of his or her life. Hypothyroid dogs who receive proper treatment
have a normal life span and are able to maintain good health well into
their golden years.
Personal Experience with Canine Hypothyroidism
At a recent Senior checkup my 12 1/2 year old Golden Retriever showed
evidence of being borderline anaemic - e.g., her red blood count (hemotocrit)
was low. One of the causes of this condition is hypothyroidism. A subsequent
T4 test confirmed the hypothesis, and after one month on the medication
her thyroid was normal and her hematocrits were also normal.
The change in her has also been dramatic. Her skin has lost its dryness
and her coat is lustrous and soft. Her energy level has also increased
substantially. She runs faster and is just generally much more eager to
walk, play, and swim. Friends who had not seen her for eight months commented
that this was a different dog from the one they remembered.
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