Very low doses of radio-iodine for hyperthyroidism. Failure to prevent a high incidence of early hypothyroidism.

One hundred and fifty-one patients with hyperthyroidism were treated with varying doses of radio-iodine (131I), and the results were analysed 1 year later. Of the patients with Graves' disease who received the lowest 131I doses (mean 2,8 mCi) 39% had persistent thyrotoxicosis and 25% were hypothyroid 12 months after therapy. Moderate doses of 131I (mean 5,9 mCi) reduced the rate of persistent disease to 19% and increased the rate of hypothyroidism by only 4% (P less than 0,05). When 131I dosages were calculated according to thyroid weight (microCi/g), patients who received the lowest doses (mean 115 microCi/g) again had significant rates of both persistent hyperthyroidism (38%) and hypothyroidism (24%). These data indicate that very low doses of 131I in the treatment of Graves's disease may result in a high incidence of persistent disease, but do not necessarily result in a very low incidence of early hypothyroidism. Low-dose 131I regimens are unsuitable for treatment of thyrotoxicosis unless very good facilities for patient follow-up are available.