TUESDAY, Jan. 20, 2004 (HealthDayNews) -- There isn't enough evidence to support routine testing for thyroid disease among adults who have no symptoms.

That's the recommendation contained in a new report from the U.S. Preventive Services Task Force. The expert panel found no convincing studies to show that asymptomatic patients do better if they begin treatment before symptoms of thyroid disease develop.

"We don't have sufficient evidence to say it isn't beneficial; we don't have sufficient evidence to say it is," says Dr. Bruce Nedrow Calonge, the panel's newly appointed chairman.

The preventive services task force, convened by the federal Agency for Healthcare Research and Quality, makes recommendations on a range of clinical preventive services. Its latest report appears in the Jan. 20 issue of the Annals of Internal Medicine.

Its core recommendation remains unchanged from 1996, when it last weighed the scientific evidence on screening for thyroid disease.

But the panel's view conflicts sharply with that of the American Thyroid Association. That group recommends measuring thyroid function in all adults beginning at age 35 with follow-up testing every five years.

The thyroid is a gland in the base of the neck that produces hormones that regulate key body functions. Almost 15 million Americans suffer from thyroid disease, according to the Thyroid Foundation of America. The most common disorders include hyperthyroidism, a condition in which the thyroid gland makes too much hormone, and hypothyroidism, when it doesn't make enough.

Women are much more likely to develop a thyroid disorder than men, according to the National Women's Health Information Center. When the thyroid isn't functioning properly, it can affect weight, energy level, muscle strength, skin health, menstrual cycle, memory, heart rate and cholesterol level, the center says.

Symptoms of an underactive thyroid include weakness and fatigue, weight gain, dry hair and skin, and increased sensitivity to the cold.

An overactive thyroid, most commonly caused by a disorder known as Graves' disease, is marked by fatigue, weight loss, nervousness, and increased sensitivity to heat. It can also cause bulging of the eyes.

Not all patients develop symptoms, especially early on, and doctors disagree about the need to identify and treat patients.

There is fair evidence, says Calonge, that the test for thyroid disease -- the thyroid stimulating hormone (TSH) test -- can detect disease in people without symptoms. But, he adds, the evidence is poor that treatment improves "clinically important outcomes."

So, is it worthwhile or not for primary-care physicians to test thyroid function in patients who have no specific symptoms or history of problems?

Dr. Mark Helfand, director of the Evidence-based Practice Center at the Oregon Health & Science University in Portland, compiled and reviewed existing studies to help the task force answer that question.

What's lacking, he says, is good data from controlled trials showing that early treatment reduces cholesterol levels, symptoms, or the risk for cardiovascular disease in patients with mild thyroid dysfunction detected by screening.

While there is plenty of evidence to show that early diagnosis and treatment of women with low bone density, for example, prevent fractures, the same standard of proof is lacking for thyroid disease, he says.

Of the studies that focus on thyroid disease, he adds, "most of them don't include asymptomatic patients at all."

More information

To learn more about the thyroid gland, visit University of Maryland Medicine. For more about thyroid diseases, check with the National Library of Medicine.

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