A comparative study of influential factors correlating with early and late hypothyroidism after 131I therapy for Graves' disease

Background I-131 therapy is recognized as the simplest, safest, least expensive, and most effective treatment, and accepted by more and more patients. However its curative effect is influenced by many factors, therefore there are some difficulties for doctors to establish individual treatment strategy. The aims of this study were to determine the incidence of early and late hypothyroidism after I-131 treatment for Graves' disease (GD) and to compare their correlation, to observe and analyze the influential factors and to understand the predictabilities of them. Methods Five hundred GD patients (144 males, 356 females; age (41.2+/-12.3) years) received I-131 treatment for the first time. The therapeutic procedure was carried out as the following: undergoing I-131 uptake test to obtain maximum of thyroid uptake value and effective half-life (EHL) time; estimating the thyroid's weight by ultrasonography; determination of thyroid hormones and correlative antibodies; pre-therapy physical examination; thyroid imaging; calculating I-131 therapeutic dosage; per os uptake of the determined I-131 dosage; follow-up appraisal of curative effect. The observing parameters included age, gender, thyroid weight, GD duration, condition of onset, state of disease, course of treatment, EHL time, maximum of thyroid uptake value, I-131 dosage and titer of correlative antibodies. We sorted out the data and used both univariate and multivariate analysis to evaluate them statistically. Results The incidence rates of early and late hypothyroidism were 33.2% and 6.6% respectively after I-131 treatment and approximately 22.2% cases of late hypothyroidism developed from early hypothyroidism. The influential factors of early hypothyroidism included course of GD, the highest thyroid uptake ratio of I-131, EHL time and thyroid microsome antibody (TMAb), etc. A multivariate analysis on late hypothyroidism showed that female patients, with recurrence after anti-thyroid drug treatment and higher thyroid weight, had lower possibility of late hypothyroidism after I-131 therapy. Conclusions The incidence of early hypothyroidism is higher than that of late hypothyroidism. The highest thyroid uptake ratio of I-131, EHL and TMAb will increase the possibility of early hypothyroidism, while GD course is the protective factor. Higher I-131 dosage, longer EHL and higher TMAb titer will also increase the possibility of late hypothyroidism. The multi-perspective and multi-factor analysis has the benefit to establish individualized treatment strategy. Chin Med J 2010;123(12):1528-1532