Health effects of therapeutic use of I-131 in hyperthyroidism

Since 1942, therapy with radioiodine ((NaI)-I-131) has gained a major role in the treatment of benign thyroid disorders, notably hyperthyroidism cause d by Graves' disease or toxic multinodular goiter. The very large series of patients treated so far offer the opportunity for an assessment of both be nign and malignant side effects. Hyperthyroidism is sometimes observed afte r radioiodine therapy due to radiation induced thyroid hormone or by an imm unological mechanism. Despite the numerous attempts to design dosage schedu les aiming at euthyroidism, hypothyroidism occurs in the majority of patien ts throughout life. Transient hypothyroidism may be observed within the fir st year after therapy and is caused by an immunological mechanism. Radioiod ine therapy in Graves' disease may induce or worsen ophthalmopathy, which c an be prevented by steroids effectively. Hypoparathyroidism and hyperparath yroidism have been reported after radioiodine therapy but probably do not e xceed the normal incidence. Sialitis is commonly observed but mostly in pat ients treated with radioiodine for thyroid cancer. There are no indications for induction of genetic abnormalities after radioiodine therapy although no definite conclusion can be reached. Much attention has been paid to mali gnant disease. In very large series, no effects of radioiodine therapy on s urvival have been observed. Some studies report an increased relative risk for certain types of cancer (notably thyroid cancer, stomach cancer, bladde r and kidney cancer or hematological malignancies). However, these observat ions were not confirmed by other large studies, so that no definite conclus ion with respect to risk for certain types of malignant disease can be draw n. However, radioiodine therapy for benign thyroid disorders has generally been considered safe and without major side effects, hypothyroidism being t he most frequent one.