SAN FRANCISCO— Treatment of asymptomatic thyroid disease is controversial but probably worthwhile, Dr. Hossein Gharib said at Perspectives in Women's Health sponsored by OB.GYN. NEWS.
Thyroid-stimulating hormone (TSH) tests are very sensitive and frequently pick up subclinical thyroid disease. The frequency of referrals for subclinical disease seems to be increasing, said Dr. Gharib, professor of medicine at the Mayo Clinic College of Medicine in Rochester, Minn. “We get a lot of consultations coming our way because of this.”
When free T4 hormone levels are normal, a TSH level below 0.5 mIU/L indicates subclinical hyperthyroidism, and a TSH level greater than 5.0 mIU/L indicates subclinical hypothyroid disease. If both the TSH and free T4 levels are abnormal, the patient has clinical thyroid disease, he said.
Make sure you have the right diagnosis before considering treatment, Dr. Gharib cautioned. A low TSH may be seen in patients who are hospitalized, have pituitary disease, or are being treated with thyroxin or amiodarone. An elevated TSH may be due to thyroid hormone resistance, rare forms of hyperthyroidism, or other causes.
He argued for treatment of subclinical hyperthyroidism because of potential cardiac, bone, and mortality benefits. The Framingham heart study showed that a TSH level below 0.1 mIU/L was associated with a 28% incidence of atrial fibrillation, triple the relative risk for atrial fibrillation seen in people with normal TSH levels during the 10-year study (N. Engl. J. Med. 1994;331:1249–52).
It is well established that accelerated bone loss seen with either clinical or subclinical hyperthyroidism (especially in menopausal women) can be arrested or reversed with treatment of thyroid disease, he added. Another long-term study shows that people with low TSH levels have an increased risk of dying, probably from cardiovascular causes (Lancet 2001;358:861–5).
He argued for treatment of subclinical hypothyroid disease to prevent progression to overt hypothyroidism, reduce symptoms, and reduce risks from increases in total cholesterol or cardiovascular problems that may accompany frank hypothyroidism. Treatment of subclinical hypothyroidism is controversial especially because it is not a life-threatening problem and usually is asymptomatic.
One study found that people with subclinical hypothyroidism who were TSH antibody positive had a 55% chance of progressing to clinical hypothyroid disease over 20 years compared with a 27% cumulative incidence of frank hypothyroidism in people with normal TSH levels who were TSH antibody positive (Clin. Endocrinol. 1995;43:55–68).
“I think that the evidence is compelling enough that we should tell the patient, 'Let's treat today so you won't become clinically hypothyroid,'” he said.
The presence of other factors should influence the decision to treat, he added. A physician may choose not to treat a healthy 35-year-old with subclinical hypothyroidism, but should strongly consider treatment in the presence of thyroid peroxidase antibodies, goiter, elevated total cholesterol, infertility, or symptoms of hyperthyroidism.
Any woman with subclinical hypothyroidism who is pregnant or thinking of becoming pregnant should be treated because even a mildly abnormal TSH level in the early stages of pregnancy can cause adverse pregnancy outcomes, Dr. Gharib said.
He suggested that women older than 30 years should get a TSH test periodically. The American Thyroid Association recommends a TSH test for women at age 35 years, to be repeated every 5 years.
Endocrine Society guidelines advise observing patients if the TSH level is 0.1–0.5 mIU/L, treating most patients with a TSH between 5 mIU/L and 10 mIU/L, and treating all patients with TSH levels that are below 0.1 mIU/L or above 10 mIU/L.
OB.GYN. NEWS is published by the International Medical News Group, a division of Elsevier.
Make sure you have the right diagnosis before you begin treatment. DR. GHARIB