Transient hypothyroidism after iodine-131 treatment of Graves' disease

One hundred twenty six patients with Graves' disease, 26 with toxic multinodular goiter, and 18 with toxic adenoma were treated with 131I (3-15 mCi), and followed at monthly intervals for six months. Transient hypothyroidism occurred at two months in 22 patients with Graves' disease. In this state TSH levels became elevated in seven patients, but were normal or suppressed in seven. In 17 patients T4 and T3 levels returned to normal without T4 replacement. Five patients developed recurrent thyrotoxicosis, and required repeated doses of 131I. The possibility of transient hypothyroidism in the early months after 131I therapy in Graves' disease should be borne in mind.