Cognitive function of elderly with subclinical hypothyroidism not improved with thyroxine replacement
Results of the Birmingham Elderly Thyroid Study showed no improvement in cognitive function for elderly patients with subclinical hypothyroidism who received thyroxine replacement.
The double blind, randomized, controlled trial included 94 patients aged 65 years and older who had subclinical hypothyroidism. The patients were recruited from a screened population in the United Kingdom.
Researchers randomly assigned the group to daily placebo or 25 mcg thyroxine (T4) replacement for 12 months. Free thyroxine and thyroid-stimulating hormone were evaluated in 8-week increments, and doses were adjusted in one-tablet increases to achieve and maintain a TSH within the reference range of 0.4 mU/L to –5.5 mU/L.
At 6 months, 82% of patients assigned to T4 replacement achieved euthyroidism. At 12 months, that percentage rose to 84%.
Cognitive function scores failed to show a significant difference between the T4 replacement and placebo groups at the 6- and 12-month tests. Patients were evaluated using the Mini-Mental State Examination, Middlesex Elderly Assessment of Mental State and Trail-Making A and B tests.
Results show “no improvement in cognitive function both in the short-term, ie when euthyroidism is achieved, and after a substantial period of time has elapsed while rendered euthyroid,” according to the researchers.
Based on these data, thyroid dysfunction screening in elderly people should not be used if the aim is to identify those with decreased cognitive function, the researchers said. Additionally, “careful consideration is indicated before treating subclinical hypothyroidism, by instituting T4 hormone replacement therapy, when such treatment may also be harmful.”
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