Care Of Your Hypothyroid Dog
You can read aother exellent article on hypothyroidism in dogs here
Ron Hines DVM PhD
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What Is Hypothyroidism ?
A sluggish thyroid gland or hypothyroidism is the most common hormone deficiency in dogs. Pets that get this problem, usually start showing signs when they are 4 - 6 years old. Male and female dogs are equally affected but I have noticed that I see it more in neutered pets. But this could be because these days, more people own neutered dogs than un-neutered dogs. Hypothyroidism probably occurs because of a combination of pet lifestyle and inborn genetic susceptibility. In some cases, we know that three genes located on your dog's chromosome 12 are involved. (ref)
Your dog's thyroid gland consists of two small lobes located near the base of its neck. This gland produces thyroxine, a hormone that regulates the body’s metabolic rate - that is the rate at which it burns calories. Think of it like the gasoline supply to your car engine. When you press down on the accelerator, the car goes faster. When the thyroid gland releases more thyroxine, the body works faster.
What Happens If My Pet's Thyroid Gland Doesn't Produce Enough Thyroxine ?
It is common for pets with hypothyroidism to gain weight while only eating moderately. These dogs have been described as “easy keepers” because they gain weight so easily.
That does not mean that most overweight dogs have thyroid disease – they are just eating too much, eating too rich a diet and get too little exercise. Many owners are oblivious to weight gain in their pets. But when an animal’s backs become flattened instead of curved and they huff and puff with every exertion some owners bring them in for a check up.
When owners bring me these pets, I run thyroid tests on all of them. The most important tests are the pet's T 4 and Free T-4 level - the levels of total thyroxine and free or active thyroxine in their blood.
How Did My Dog Become Hypothyroid ?
Most cases of hypothyroidism are caused by the dog’s own immune system attacking its own thyroid gland tissue. This condition is called autoimmune thyroiditis (the anti-thyroid antibody test can be used to confirm this). This type of hypothyroidism is further broken down into two types, lymphocytic thyroiditis and idiopathic thyroid atrophy. In many ways this problem in dogs is similar a problem that occurs in humans. You can read about that one here. In both cases, the gland fails to produce enough of the hormone, thyroxine. It really doesn't matter which type your pet has because the signs and treatment are the same. We know that genetics plays an important role in this disease. (ref) That is why hypothyroid dogs and close relatives of hypothyroid dogs should not be bred. Occasionally, a puppy will be born a dwarf. It is common for dwarf puppies to have been born with hypothyroidism. (ref1, ref2) It is also one of the few situations where cats suffer from hypothyroidism as well. (ref)
What Breeds Of Dog Are Commonly Affected ?
I see Hypothyroidism most commonly in Labrador and Golden Retrievers, Dachshunds, Cocker Spaniels, Boxers Doberman Pinchers and Greyhounds - in that order of frequency. I rarely encounter this disease in terriers or other toy breeds but they do occasionally develop the problem. Hypothyroidism also occurs somewhat more frequently in spay female and male dogs than in intact pets. (ref)
What Changes Might I See In My Pet's Skin And Haircoat ?
The pet’s hair coat is often scurfy, flaky and dull. The coat often lacks finer body hairs and undercoat. Your pet's tail may become as bald as a rat’s tail. An important clue pointing to thyroid deficiency is that this hair loss is not itchy as it would be if the pet had fleas , allergic skin or infectious skin disease.
Hypothyroid dogs commonly have excess black pigment in the skin of their groin. This pigment results in a condition similar to one that occurs in humans for other reasons, acanthosis nigricans. Sometimes this pigment is present over much of the body and the skin becomes oily and thickened. Broken toenails and toenail infections are common in hypothyroidism. Your pet's hair coat color may change.
What About Reproductive Problems and Infertility ?
Yes, Female dogs with hypothyroidism often cycle erratically and fail to get pregnant, have small liters or miscarry. It also affects male fertility. Hypothyroid male dogs may have low sperm levels and decreased libido. Pseudopregnancy or false pregnancy with milk flow and abdominal distension is common in these dogs (especially dachshunds). Hypothyroidism should never be corrected for the purpose of breeding these dogs.
Are There Other Signs Of Hypothyroidism I Might Recognize ?
Yes, your pet might not act as bright as it once did. Hypothyroidism affects mental alertness and the ability to learn. You might also notice that your pet is more sensitive to cold and chilly weather.
A slow heart rate, constipation, anemia, muscle weakness and atrophy, nerve disturbances, edema, stunted growth, and slowed clotting of the blood can also be signs of hypothyroidism.
Hypothyroid dogs have more than their fair share of joint pain and swelling and ear and skin infections. You can read about those ear infections here. Lazy behavior – such as increased sleeping, less play activity and easy fatigue can also indicate thyroid disease. It has also been reported that hypothyroid dogs have more “dry eye” disease (keratoconjunctivitis sica).
What Test Can My Vet Run On My Pet To Diagnose Hypothyroidism ?
The Thyroid Panel includes tests to determine the level of three forms of thyroid hormone (T-4, free T-4 and T-3). I will occasionally also run at thyroglobin auto-antibody test to determine if autoimmune thyroid disease is present.
It is important to understand that other health problems in your pet can cause the test results to be low. So before treatment is begun, the pet's general health needs to be completely examined.
Blood levels of T-4 are normally about 1.0-4.0 micrograms/deciliter. Normal levels of T-3 are 45-150 nanograms/decileter and normal levels of Free T-4 are 11-43 picomols/leter. I become suspicious of hypothyroidism when the numbers for T-4 hover at about one unit and T-3 and Free T-4 levels are low-normal - even if the lab reports the case as normal. Falsely low thyroid hormone levels can be due to administration of steroids (cortisone-like medications) or concurrent systemic disease. A TSH stimulation test can be run if the diagnosis is in doubt. In borderline cases, sometimes, the best approach is to provide the pet with a small thyroid supplement for 30 days and just see if it improves. However, there are risks in this approach. If thyroxine levels become too high, other body organs can be damaged. So this approach needs frequent monitoring of your pet's blood thyroxine level.
One must be cautious in diagnosing hypothyroidism in sight hounds (greyhounds, Italian greyhounds, whippets, salukis). These breeds seem to naturally have lower thyroid hormone levels than other dog types. (ref)
What Medications Are Available To Help My Pet ?
Fortunately, thyroid hormone is available in inexpensive tablet form. I generally prescribe the T-4 form of the hormone, l-thyroxine (levothyroxine sodium). All dogs need their dose individually tailored to their needs. Signs that the initial dose may be too high are agitation, excessive thirst, and diarrhea. When these occur the dose needs to be lowered. Thirty days after beginning treatment, I assay a second blood sample for Free T-4. If levels are still not adequate the dose is increased. I then retest the dog every six months. Once a dog is placed on medication, it should be given for the rest of the pet’s life. Each veterinarian will have their own opinion as to dose and treatment plan, based on what has worked best for them in the past.
When the disease is diagnosed early and treated faithfully, you can expect your pet to live a long and happy life.