Principle: Autonomously functioning thyroid nodules secrete excess thyroid hormone, which inhibits TSH secretion from the pituitary gland. The decrease in TSH levels decreases the uptake of iodine-131 by normal thyroid tissue outside the nodule. When a patient is given a therapeutic dose of iodine-131, the autonomously functioning nodule takes up a large amount of iodine-131, and the b-rays emitted by iodine-131 exert a therapeutic effect, causing the nodule to shrink or disappear. The suppressed normal thyroid tissue takes up no or very little iodine-131, receives a small amount of irradiation, is not damaged, and subsequently regains its function. Indications: Autonomous functional thyroid nodules with arrhythmia, atrial fibrillation, contraindications to surgery or unwillingness to undergo surgery. Contraindications: Pregnant and lactating patients; those with a predisposition to malignant lesions in the thyroid gland; those with a low rate of iodine-131 uptake in autonomously functioning nodules. Treatment 1. Patient preparation: Preparation is basically the same as for iodine-131 treatment of hyperthyroid Graves’ disease, but measures should be taken to protect the normal thyroid tissue outside the nodules. When iodine-131 thyroid imaging suggests that the extra-nodular thyroid tissue is not completely suppressed, exogenous thyroid hormone should be used to inhibit its uptake of iodine-131 until another iodine-131 image confirms that the extra-nodular thyroid tissue does not uptake iodine-131, and then treatment can proceed. Stop anti-thyroid medication before treatment to prevent endogenous TSH elevation. In patients who have used TSH for diagnostic purposes, iodine-131 treatment should be administered after 2 weeks. 2. Determination of iodine-131 dose: The standard dose method is used, iodine-131 15-30mCi (555-1110MBq) is given at once, while it can be increased or decreased as appropriate with reference to nodule size, effective half-life, iodine-131 uptake rate and patient condition. 3. Follow-up: Autonomous functional nodules gradually shrink in 2~3 months after iodine-131 treatment, and the symptoms and signs of hyperthyroidism gradually improve. 3~6 months later, thyroid imaging shows the disappearance of hot nodules and the restoration of normal thyroid tissue function outside the suppressed nodules; or the nodules become smaller and the function of surrounding normal thyroid tissue is not fully restored. If the patient is not cured after 6 months, re-treatment with iodine-131 can be considered.