Overlooked, underdiagnosed? Thyroid disease poses a challenge

For such a small gland, the thyroid is certainly causing a big flap. There is conflicting advice over how widely to screen for asymptomatic thyroid disease: Everyone? Pregnant women? People older than 35? Women older than 60?

When it comes to determining an answer, "there is chaos in the medical community," says Terry Davies, MD, professor of medicine at Mount Sinai School of Medicine in New York and director of the division of endocrinology.

And even when patients complain of symptoms that could signal a dysfunction in the thyroid, the problem is still being missed, some endocrinologists say.

Thus that butterfly-shaped regulator of metabolic processes presents primary care doctors with a peculiar conundrum. They are well aware of the range of disorders that affect the thyroid, but there is still considerable debate about patients who slip through the cracks. Add to this a growing discord over screening, and this small gland becomes more complicated.

For starters, the slow onset of the vague symptoms that can accompany the most common form of thyroid disease, hypothyroidism, trips up many primary care physicians who are swamped every day with patients who are fatigued, depressed or gaining weight, says Paul Ladenson, MD, professor and director of endocrinology and metabolism at Johns Hopkins Medical Institutions. He estimates that almost half the people with thyroid dysfunction are not properly diagnosed.

Donald Bergman, MD, president of the American Assn. of Clinical Endocrinologists, includes a swipe at the nation's health care system. "Why aren't people doing a simple blood test to figure out if patients have mild thyroid disease before they get symptomatic?" he said.

"You name an illness and I'll give you a bad statistic. Do you know how many people with osteoporotic hip fractures are treated for osteoporosis? Fewer than 30%. You would agree that lowering your cholesterol level is good for your heart? Do you know what's happened to the overall cholesterol levels in this country over the last 10 years? Nothing."

Treating an illness before it happens or at least before it progresses is not how American medicine works, Dr. Bergman continues. "It's not the way insurance works. It's not the way Medicare works."

Thyroid dysfunction is most often mistaken for a psychiatric disease, says Dr. Davies. When the thyroid is overactive, it's mistaken for anxiety. When it's underactive, it's mistaken for depression.

"It's not unusual for patients to get passed from doctor to doctor before anyone gets the message."

There is strong evidence that thyroid diseases are common. Researchers tested the blood levels of thyroid stimulating hormone in 26,000 visitors to a statewide health fair in Colorado and determined that nearly 10% had an undetected abnormality -- double the number of people thought to have a dysfunctioning thyroid. That research was published in the Feb. 28, 2000, Archives of Internal Medicine.

The researchers also found that nearly 40% of those who were taking thyroid medication still had abnormal TSH levels, indicating a need for closer monitoring.

More than eight out of 10 patients with thyroid disease are women. "There are a tremendous number of women who are on thyroid supplements because their thyroids just aren't functioning adequately," says Mary Jo Welker, MD, chair and professor of clinical family medicine at Ohio State University College of Medicine and Public Health in Columbus.

But Dr. Welker would beg to differ that most symptomatic patients are not referred for tests. "When patients come in and they're depressed or tired one of the first things [physicians] try to check for is thyroid disorder. They are checking for people who have symptoms, not screening for people who don't have symptoms."

Treatment is more clear cut

Even if it isn't easy to decide who to screen, at least the TSH test provides a straightforward way to make the determination to treat. "The only hard part about making the diagnosis of an underactive or overactive thyroid gland is thinking about the possibility," Dr. Ladenson says. "Once that occurs, it's very easy in the laboratory to rule these disorders in or out."

The TSH test, which actually measures a pituitary gland hormone, has made a big difference in checking the thyroid's role in the body's feedback system that links the hypothalamus, pituitary and thyroid. Although it has been around for several years, the sensitivity of the newer versions of the test have improved enormously, Dr. Bergman said.

Thyroid diseases are often treated and monitored by primary care physicians, who should be on the alert that patients can ask for TSH tests now that the American Assn. of Clinical Endocrinologists and the American Thyroid Assn. launched a joint campaign to highlight Thyroid Awareness Month in January. Their campaign urged everyone older than 35 to ask their physicians for TSH blood tests.

But that advice runs counter to recommendations against widespread screening that were made in two separate reports released in January. One review of existing data, published in the Jan. 14 JAMA, led a panel of doctors to recommend against routine population screening for subclinical thyroid disease because of the lack of evidence to support benefit.

That panel did recommend screening and treatment for women who are pregnant or older than 60, as well as others at high risk. Thyroid disease is associated with poor outcomes in pregnancy, and its prevalence is known to increase in older women.

Meanwhile, the U.S. Preventive Services Task Force tackled the issue and also reported in January that existing evidence is insufficient to recommend either for or against routine screening for thyroid disease in adults.

With the screening question open, physician judgment rules. "It is basically left up to the individual physician, which is as it should be," Dr. Bergman says.

Which patients are screened and treated may depend on training. Physicians who specialize in thyroid disease are much more likely to place a high priority on screening, Dr. Welker says. "But the evidence doesn't really support screening asymptomatic patients." The American Academy of Family Physicians recommends against routine thyroid screening in asymptomatic patients younger than 60.

At the very least every woman either before pregnancy or in early pregnancy should have her thyroid tested, Dr. Davies advises. "It's been four years since I wrote an editorial asking why aren't the medical associations saying every woman in early pregnancy should be screened for thyroid disease. But it's still not standard of care."

Dr. Davies would go even further and incorporate thyroid tests into all routine medical exams. But he allows that cost is an issue. Labs charge $40 to $50 for the test, and when you multiply that by 100 million people, it adds up quickly.

Dr. Welker agrees that the cost would be high, and because guidelines don't recommend routine screenings, insurance companies don't generally cover them.

But Dr. Ladenson studied the cost-effectiveness of screening all adults older than 35 every five years for thyroid disease and found that thyroid screening rivaled the cost-effectiveness of screening for high cholesterol.

He would like to see a blood test for thyroid disease added to the recommended schedule of check-ups and cholesterol screenings.

Conditions to prevent

Thyroid disorders are best detected early before they can trigger other medical problems. The thyroid hormone affects virtually all metabolic processes; too much speeds up metabolism, while too little slows it down.

Studies have found that even a slight decrease in thyroid function could increase cholesterol levels. "So patients cannot know what their correct cholesterol is until their thyroid has been repaired," Dr. Davies says.

Thyroid failure leads to retained fluid, which even can trigger carpal tunnel syndrome among those who have a propensity for it, he adds.

Thyroid disease is particularly dangerous during pregnancy. Thyroid hormone is critical for the baby's brain development. Hypothyroidism has been associated with maternal anemia and myopathy in pregnant women. Hyperthyroidism has been associated with premature infants and preeclampsia.

Treatment for hypothyroidism by replacement thyroid hormone can quickly lead to dramatic improvements, Dr. Bergman says. "The classic expression is, 'The fog has lifted.' "

There are three unappealing choices for an overactive thyroid, Dr. Davies explains. "You can cut the gland out, destroy it with radioactivity or provide tablets that have some potential side effects. In my practice I start almost everyone on the tablets."

In November 2002, AACE published revised guidelines that narrowed the range for normal thyroid function from the old TSH of 0.5 mIU/L to 5.0 mIU/L, to 0.3 mIU/L to 3.0 mIU/L.