ATA News Release 2004

Hyperthyroid Patients Receiving Thyroid Hormone Therapy
After Radioiodine Treatment Have Reduced Risk of Death

(VANCOUVER, BC, Oct. 1, 2004)—An increased risk of cardiovascular-related and overall deaths is found in patients treated with radioiodine (I-131) for hyperthyroidism — an overactive thyroid. This almost certainly relates to the thyroid dysfunction itself and not treatment or other factors, according to a new study being presented on Friday, Oct. 1, at the 76th Annual Meeting of the American Thyroid Association in Vancouver, British Columbia, Canada.

Past research has shown that at least half of all patients treated with I-131 will eventually develop an underactive thyroid, as indicated by a low level of the thyroid hormone thyroxine (T4) in the blood and elevated thyroid-stimulating hormone. The resulting hypothyroidism requires T4 replacement therapy.

“In our study, the excess risk of cardiovascular deaths was confined to the period before these patients became hypothyroid,” said Jayne A. Franklyn, MD, PhD, Professor of Medicine in the Division of Medical Sciences at the University of Birmingham and Queen Elizabeth Hospital in
Birmingham, United Kingdom, “which is a consequence of their radioiodine treatment, and, therefore, before they needed to begin thyroxine replacement.”

“We can speculate,” she added, “that the increased risk of vascular deaths was seen only in the patients before they became hypothyroid because developing an underactive thyroid is an indicator of the complete cure of hyperthyroidism, which is the best way of removing the adverse impact of the disease.”

In 1998, Dr. Franklyn and colleagues reported in the New England Journal of Medicine that death from all causes and cardiovascular events significantly increased in patients treated in the past for hyperthyroidism with I-131. Therefore, with the current study, they wanted to find out the influence of developing hypothyroidism — and its treatment with T4 — on the increased death rate.

In the latest study, they examined the records of 2,668 patients over the age of 40 who had received
I-131 from 1984–2002. Mortality data up to the end of 2003 were obtained from the UK Office for National Statistics. The researchers compared the death rate of the study group with age, sex, and period-specific data for all others living in England and Wales. Dr. Franklyn and her colleagues once again found an increased mortality from circulatory diseases, including both cardiovascular diseases, especially rhythm abnormalities and heart failure, and cerebrovascular diseases, such as stroke. However, in this study, they also found that the increase in all-cause mortality was confined to individuals who had not required T4 or before T4 therapy had begun.

“In general, we need to be aware that our thyrotoxic patients are at increased risk of vascular deaths,” warned Dr. Franklyn. “It may be that prompt treatment with radioiodine to ensure complete cure of hyperthyroidism is the best way to remove this risk, although this specific question needs to be investigated in further studies.”

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