Chicago, IL - A long-term follow-up of more than 3000 elderly persons found no link between subclinical hyperthyroidism or hypothyroidism and risk of cardiovascular events or mortality, casting doubt on prior evidence to the contrary [1]. But the community-based study, reported in the March 1, 2006 issue of the Journal of the American Medical Association, did confirm the long-recognized increased risk of atrial fibrillation (AF) associated with subclinical hyperthyroidism.

We say there's no evidence, based on our data, that screening would benefit the population.

"Many patients with mild thyroid problems are being treated now and it's not clear if it's actually helping them," according to Dr Anne R Cappola (University of Pennsylvania, Philadelphia) as quoted in a press release from her institution. The lead author of the study, she said her team's data suggest that "if you do find someone over the age of 65 with a mildly overactive thyroid, they should be treated." However, she added, "There's no evidence you should treat someone with a mildly underactive thyroid to help deter cardiovascular disease."

Although some societies recommend periodic screening for abnormal thyroid-stimulating hormone (TSH) levels in certain groups, Cappola continued, "We say there's no evidence, based on our data, that screening would benefit the population."

Endocrinologist Dr David S Cooper (Sinai Hospital of Baltimore, MD) agrees that there's little or no good evidence that treatment of subclinical hypothyroidism would prevent death or cardiovascular events. Still, he told heartwire, "I think we would probably all treat it," largely to address any dyslipidemia or constitutional symptoms or to prevent progression to overt hypothyroidism.

Cooper, a JAMA contributing editor, said the large Cappola study, with its long follow-up and thorough adjudication of patient records, was "very carefully done" and "more definitive" than prior observational studies of the same issue. "It's still very controversial," he said, "and until there are prospective trials taking people like those in this study and randomizing them to be treated or not, we're never going to know the answer. But I'm not sure that such a study will ever be done."

The group studied 3233 persons aged >65 years with evaluable TSH levels followed from 1989 to 2002 as part of the Cardiovascular Health Study (CHS), conducted in four US communities. Subjects with known or suspected thyrotoxicosis were excluded. Over a mean of 12.5 years, TSH activity wasn't significantly associated with mortality or CV outcomes.

All-cause mortality was significantly increased (p=0.02) among subjects with subclinical hyperthyroidism compared with euthyroidism, but the difference became nonsignificant after adjustment for age and sex, the group writes.

The analysis supports the treatment of subclinical hyperthyroidism in the elderly to prevent AF, according to the group. But it also suggests that thyroid-disease screening solely for AF prevention would yield too few cases to be practical, they write.

Important, although not emphasized by the authors, is the observation that subclinical hyperthyroidism seems to promote AF in people with TSH levels above 0.1 mU/L, according to Cooper. "Here they show for the first time that even when TSH levels are just a little bit below normal, between 0.1 and about 0.5 [mU/L], there's still a higher frequency of atrial fibrillation." One implication of that finding, he said, is that perhaps measures should be taken to prevent arrhythmia in elderly patients with hyperthyroidism that is even milder than what is currently treated.