MONTREAL – Amid common patient concerns about weight gain in the treatment of hyperthyroidism, findings from a large study suggest the therapy with the most favorable survival rate – radioiodine – is not associated with an increased risk of weight gain or obesity.
“EGRET is the first large study using population-based linked community and hospital data to elucidate the long-term consequences of treatment modalities for hyperthyroidism,” said co-author Kristien Boelaert, MD, PhD, while presenting the research at the American Thyroid Association annual meeting.
“The administration of [radioiodine] for hyperthyroidism is associated with a survival benefit for patients with hyperthyroidism and is not associated with increased risks of becoming obese,” Dr. Boelaert, a professor of endocrinology and consultant endocrinologist with the Institute of Applied Health Research, University of Birmingham, England, told this news organization.
However, “overall, there was a nearly 10% risk of major adverse cardiac events [MACE] in patients with hyperthyroidism regardless of the treatment modality used,” she noted.
Commenting on the findings, Jonathon O. Russell, MD, said the study offers surprising – but encouraging – results.
The discovery that radioiodine shows no increase in weight gain “contradicts numerous previous studies which have consistently demonstrated weight gain following definitive radioiodine,” Dr. Russell told this news organization.
Overall, however, “these findings reinforce our knowledge that definitive treatment of an overactive thyroid leads to a longer life – even if there is some weight gain,” added Dr. Russell, who is chief of the Division of Head and Neck Endocrine Surgery at Johns Hopkins, Baltimore.
Hyperthyroidism associated with serious long-term cardiometabolic issues
Hyperthyroidism is associated with serious long-term cardiovascular and metabolic morbidity and mortality, and treatment is therefore essential. However, the swing to hypothyroidism that often occurs afterward commonly results in regaining the weight lost due to the hyperthyroidism, if not more, potentially leading to obesity and its attendant health risks.
To investigate those risks in relation to the three key hyperthyroidism treatments, the authors conducted the EGRET trial. They identified 62,474 patients in the United Kingdom population-based electronic health record database who had newly diagnosed hyperthyroidism and were treated with antithyroid drugs (73.4%), radioiodine (19.5%), or thyroidectomy (7.1%) between April 1997 and December 2015.
Exclusion criteria included those with less than 6 months of antithyroid drugs as the only form of treatment, thyroid cancer, or pregnancy during the first episode.
With a median follow-up of about 8 years, those who were treated with thyroidectomy had a significantly increased risk of gaining weight, compared with the general population (P < .001), and of developing obesity (body mass index > 30 kg/m2; P = .003), while the corresponding increases with antithyroid drugs and radioiodine were not significantly different, compared with the general population over the same period.
In terms of survival, with an average follow-up of about 11 years per person, about 14% of the cohort died, with rates of 14.4% in the antithyroid drug group, 15.8% in the radioiodine group, and 9.2% in the thyroidectomy group.
Mortality rates were further assessed based on an average treatment effects analysis in which the average change was estimated, compared with the index of antithyroid drugs – for instance, if all were treated instead with radioiodine. In that extension of life analysis, those treated with radioiodine could be expected to die, on average, 1.2 years later than those taking antithyroid drugs (P < .001), while those treated with thyroidectomy would be expected to die 0.6 years later, which was not statistically significant.
Using the same average treatment effects analysis, Dr. Boelaert noted, “we found a slightly increased risk of major adverse cardiovascular events following radioiodine, compared with antithyroid drugs; [however], the risk was very small and may not be clinically relevant.”
“Previous data from our and other groups have shown reduced risks of mortality and cardiovascular death following radioiodine-induced hypothyroidism, although this is not confirmed in all studies.”