In the present study, we have investigated mortality in a cohort of individuals treated with radioiodine for hyperthyroidism and examined the effect of T 4 treatment for radioiodine-induced overt hypothyroidism on mortality. In view of uncertainty about the effect of subclinical thyroid dysfunction on circulatory mortality risk, we also examined the influence of subclinical hypothyroidism and subclinical hyperthyroidism after radioiodine treatment.
The study participants were all patients who had been treated for hyperthyroidism in the West Midlands region of England during the years through and for whom serum thyrotropin and free T 4 concentrations had been recorded since when measurement of serum thyrotropin using a sensitive assay was introduced.
Participants treated as recently as were included in view of our previous finding of increased all-cause and circulatory mortality within the first year after treatment. Demographic data and information regarding the date, dose, and number of radioiodine treatments, serial measurements of serum free T 4 and thyrotropin, and date of initiation of T 4 therapy were recorded in the Birmingham Thyroid Follow-up Register, which was established in the s to ensure regular biochemical testing of patients treated with radioiodine and detection of hypothyroidism after treatment.
The register has been described elsewhere. The first recorded thyrotropin measurement was at this time. Other data, including risk factors for vascular disease, were not recorded on the Thyroid Follow-up Register and have not been analyzed in the present study. The initial cohort comprised patients. Four were excluded because date of birth was unknown, 10 because date of first thyrotropin treatment was unknown, and 53 were recorded as emigrated or not traced by the Office for National Statistics.
Those in the cohort for whom a biochemical test result was recorded during were deemed alive. For the remainder of the final group of patients, demographic data were sent to the UK Office for National Statistics for tracing in the National Health Service Central Register to determine vital status on December 31, For those who had died before that date, death certificates were obtained and underlying cause of death coded by Office for National Statistics according to the 9th or 10th revision of the International Classification of Diseases ICD-9 or ICD Comparison of Mortality With Background Population.
The cause of death for each patient who had died was compared with age-, sex-, and year-specific mortality data from England and Wales, recorded in the World Health Organization data bank. The number of person-years at risk, contributed by each patient in the study, was calculated from the date of first serum thyrotropin measurement recorded on the register approximately 12 months after euthyroidism was restored after radioiodine treatment to the census date of December 31, , or until the date of death.
The expected number of deaths was calculated by multiplying the number of person-years in each stratum defined according to age, sex, and calendar year by the corresponding mortality rate for that age, sex, and period in England and Wales. The standardized mortality ratio SMR, the ratio of observed to expected deaths was used to estimate the relative risk. Similarly, we calculated the expected number of deaths during the period prior to or not requiring T 4 treatment, and during the period receiving T 4 treatment, based on the number of person-years accumulated not receiving and receiving T 4 treatment and calculated SMRs as described above.
Age-specific mortality rates for all causes of death were calculated for both sexes during follow-up prior to, or not requiring, T 4 treatment or during the period of T 4 treatment, and compared them with mortality rates for the background population. A similar method to that described above was used to calculate SMRs during the period of follow-up prior to T 4 therapy specifically associated with mild hypothyroidism , defined as increased serum thyrotropin levels ; euthyroidism , normal serum thyrotropin levels; or mild hyperthyroidism , low serum thyrotropin.
Comparison of Mortality Within the Cohort. A time-dependent Cox proportional hazards-regression model was used to evaluate the prognostic influence of T 4 therapy and of serum thyrotropin measurements on survival. We also investigated differences in risk associated with subclinical thyroid dysfunction recorded during follow-up before initiation of T 4 therapy for overt hypothyroidism. For this, we considered both the first recorded thyrotropin measurement as a single time-constant categorical variable low, normal, or high serum thyrotropin levels , as well as repeated measures of serum thyrotropin considered as time-dependent categorical variables.
These models were adjusted for patient age at entry in 5-year age groups , sex, and interval between radioiodine treatment and date of first serum thyrotropin measurement. Before presenting results from the Cox models, we tested the proportional hazard assumption by introducing constructed time-dependent variables for all covariates and tested for their significance. Kaplan-Meier curves were constructed for survival from ischemic heart disease during the period of follow-up prior to T 4 therapy and predicted by the first recorded serum thyrotropin measurement low, normal, or high.
Data were analyzed using SAS version 8. All P values were 2-sided. Characteristics of the patients in the study are shown in Table 1. Their median age at first measurement of serum thyrotropin was 62 years range, years and The baseline characteristics of men and women were similar Table 1. Of the patients, died before the end of the study. The expected number of deaths for the total number of person-years at risk 15 years was , leading to a relative risk of 1.
The risks of death due to endocrine and metabolic disorders and circulatory diseases were significantly greater than what they were in the general population and together accounted for 47 of the 67 excess deaths observed.
The risk of death from other major causes, including cancer and respiratory diseases, were not increased significantly Table 2. Excess deaths from circulatory diseases were confined to cardiovascular deaths SMR, 1.
There were also small and nonsignificant increases in the number of deaths from ischemic heart disease and cerebrovascular disease. When mortality among men and women was considered separately, the increase in all-cause, circulatory, and cardiovascular risk was confined to women; in men an increase in deaths from respiratory diseases was apparent Table 2.
Mortality was compared during follow-up specifically associated with no T 4 therapy ie, in those never overtly hypothyroid and requiring T 4 or prior to development of overt hypothyroidism with follow-up specifically during treatment with T 4 for overt hypothyroidism. All-cause mortality was increased in the cohort compared with the background population of England and Wales when not taking, or before commencement of, T 4 therapy. This excess mortality was no longer evident when risk of death for the cohort compared with the background population was considered for the period of follow-up during T 4 therapy Table 3.
This difference largely reflected a difference in risk of death from circulatory diseases, and specifically from death due to cardiovascular diseases, especially the subcategory that included deaths from dysrhythmias and heart failure, as well as cerebrovascular diseases Table 3. A similar pattern was observed when mortality was examined in men and women Table 3 and when the cohort was stratified according to age data available on request.
Age-specific mortality rates for all causes of death and for both sexes, compared with the background population of England and Wales, for the period of follow-up prior to, or not requiring, T 4 and follow-up associated with T 4 therapy are shown in Figure 1.
This illustrates an increase in all-cause mortality associated with follow-up prior to T 4 , not evident during follow-up associated with T 4 therapy. The absence of increased risk of death from all causes or from vascular diseases in the cohort when taking T 4 therapy was sustained, being evident both in the first 5 years after starting T 4 circulatory disease SMR, 0.
The results were similar when comparison within the cohort was performed using a multivariable Cox proportional hazards regression model including T 4 therapy as a time-dependent covariable Table 4. All-cause mortality was decreased during follow-up of patients receiving T 4 therapy compared with risk during follow-up when not taking T 4 therapy hazard ratio, 0. Find out if clinical studies are right for you. Griffin P. Rodgers explaining the importance of participating in clinical trials. You can view a filtered list of clinical studies on hyperthyroidism that are open and recruiting at www.
You can expand or narrow the list to include clinical studies from industry, universities, and individuals; however, the NIH does not review these studies and cannot ensure they are safe. Always talk with your health care provider before you participate in a clinical study. The NIDDK translates and disseminates research findings to increase knowledge and understanding about health and disease among patients, health professionals, and the public.
Hoang, D. How common is hyperthyroidism? Who is more likely to develop hyperthyroidism? Is hyperthyroidism during pregnancy a problem? What are the complications of hyperthyroidism? What are the symptoms of hyperthyroidism? What causes hyperthyroidism? How do doctors diagnose hyperthyroidism? How do doctors treat hyperthyroidism? How does eating, diet, and nutrition affect hyperthyroidism? Clinical Trials for Hyperthyroidism What is hyperthyroidism? The thyroid is a small gland in your neck that makes thyroid hormones.
About 1 out of Americans ages 12 years and older have hyperthyroidism. Be sure your hyperthyroidism is under control before becoming pregnant. Symptoms of hyperthyroidism can vary from person to person and may include 4 weight loss despite an increased appetite rapid or irregular heartbeat nervousness, irritability, trouble sleeping, fatigue shaky hands, muscle weakness sweating or trouble tolerating heat frequent bowel movements an enlargement in the neck, called a goiter In older adults, hyperthyroidism is sometimes mistaken for depression or dementia.
Overactive thyroid nodules Overactive thyroid nodules, or lumps in your thyroid, are common and usually not cancerous. Thyroiditis Thyroiditis is inflammation of your thyroid gland. The types of thyroiditis that can cause hyperthyroidism include subacute thyroiditis, which involves a painfully inflamed and enlarged thyroid. Your thyroid may be enlarged. However, when the gland is underactive a condition called hypothyroidism , associated with too little thyroxine or overactive a condition called hyperthyroidism , associated with too much thyroxine , it can wreak havoc on your body.
Scientists have long known that thyroid problems that stem from an imbalance of its hormones may be associated with subsequent heart problems , from an irregular heartbeat to cardiovascular disease. Now, they've added sudden cardiac death to that list of potential heart problem connections, according to a new study published in the journal Circulation on Tuesday.
Read More. Layal Chaker, research fellow in endocrinology and epidemiology at Erasmus University Medical Center Rotterdam in the Netherlands, lead author of the study. However, it was not known that higher thyroid hormone levels could also be a risk factor for sudden cardiac death," she added. Sudden death risk? The current study involved health data on 10, adults, ages 45 and older, from Rotterdam. Infection or another illness, certain medications, or exposure to extreme cold can trigger myxedema in someone with an underactive thyroid.
Your doctor will prescribe an initial dose of synthetic thyroid hormone medication and re-test the level of thyroid stimulating hormone TSH in your blood in approximately six to eight weeks, Dr.
Kao explains. Doing so at the same time every day works best to keep your thyroid hormone level consistent. Getting diagnosed and starting treatment are key elements of getting this condition under control. Treatment for underactive thyroid is effective and relatively simple, and a number of health problems and potentially serious complications can be avoided.
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