Hypothyroidism: the Quiet Threat

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Underactive thyroid can masquerade as normal aging

Fred, a 6-year-old golden retriever, hasn't been himself lately. He spends less time playing and a lot more time curled up by the fire. His coat is looking dry and thin. His owners wonder: Is Fred just getting old, or is he sick?

There's no way of knowing for sure without a veterinary exam. But one of the first things that would flash through my mind would be hypothyroidism.

You may have heard of hypothyroidism because it's fairly common in humans. As it turns out, it's widespread in dogs too. In fact, hypothyroidism is the most common glandular disorder in dogs. (Cats, on the other hand, almost never develop this illness.)

A healthy thyroid gland produces hormones that are vital to the proper functioning of every cell in the body. But in hypothyroidism, the thyroid's production slows or even stops. Hypothyroidism is more common in some breeds, so it is suspected that there is a genetic cause.

Hard to Spot--Easy to Treat
Because the slowdown is gradual and symptoms often don't appear until a dog is in middle age (3 to 8 years old), many an owner has blamed the effects of hypothyroidism on the aging process. It's no wonder. Hypothyroidism's most common symptoms mimic the changes that many dogs undergo as they get older.

Lethargy
Weight gain
Difficulty staying warm
Dry, flaky, greasy, or smelly coat and/or ears
Ear infections
Hair loss on the trunk or tail (but not the legs or head)
If left untreated, the disease seldom kills a dog, but it can make his life miserable. Underactive thyroid can impair the function of the brain, eyes, heart, and gastrointestinal system.

Once you identify it, though, treatment for hypothyroidism is simple and very effective in most cases. In fact, with proper treatment, dogs with an under-active thyroid have normal lifespans and recover completely. All they need is a thyroid supplement, usually taken in pill form twice daily. Some symptoms disappear quite quickly (lethargy may improve in a week). Other symptoms, such as hair loss, may take several months to reverse.

Putting It to the Tests
The most challenging part of hypothyroidism is making the diagnosis. Many people-dog owners and vets alike-don't know about the latest generation of diagnostic blood tests. Vets used to count on blood tests called Total T3 and Total T4, which checked the amount of thyroid hormone in the bloodstream. But recent research has shown that these tests are not very accurate for diagnosis.

Now there's a better way: a series of three additional tests called serum Free t4, canine tsH concentration, and thyroglobulin autoantibodies. All are highly accurate. And while they can cost a little bit more than the older approach, they're still affordable. (At the American Society for the Prevention of Cruelty to Animals [ASPCA] in New York City, the cost for the series is $35.)

Which dogs need the new tests? I asked Arnold Plotnick, DVM, chief of staff at the Bergh Memorial Animal Hospital of the ASPCA in New York City. If a dog shows symptoms of hypothyroidism, a Total T4 should be performed initially, as a preliminary screening, along with several other very useful tests such as a complete blood count, general chemistry screen, and urinalysis, says Dr. Plotnick. This will help rule out diseases that may cause similar symptoms and also provide a clue as to whether the thyroid is an issue. If the Total T4 test is low-normal or low, you should ask your veterinarian about having your dog get the three new tests.

Breeds at Higher Risk
Hypothyroidism can strike any dog and affects males and females equally. Some breeds do run a higher risk however. Golden retrievers, Doberman pinschers, dachshunds, shelties, Irish setters, Pomeranians, miniature schnauzers, cocker spaniels, and Airedales are among those.

PHOTO (COLOR): If he seems more than just down in the dumps, consider thyroid screening

PHOTO (COLOR): Amy Marder, VMD

ILLUSTRATION

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by Amy Marder, VMD, Clinical assistant professor at the Tufts University School of Veterinary Medicine and vice president of Behavioral Medicine and Companion Animal Services at the ASPCA Headquarters in New York City

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