Long-term results from graded low dose radioactive iodine therapy for thyrotoxicosis.

An analysis has been made of the results of treatment in a series of 261 consecutive patients given graded low dose radioactive iodine therapy for thyrotoxicosis. Of these patients, 140 (54%) became euthyroid after a single dose of 131I and a further 50 (19%) achieved a remission after supplementary treatment with an antithyroid drug; 45 patients (17%) required further treatment with 131I which was invariably curative. The incidence of hypothyroidism was 10% at 1 year. The subsequent incidence of hypothyroidism in the whole group was 27% at 5 years, 40% at 10 years and 53% at 15 years. Patients continued to become hypothyroid at a constant rate of 3% per year. The incidence of early hypothyroidism can be reduced to some extent by using low doses of 131I and by relating the dose to the size of the gland. Late hypothyroidism on the other hand is due to latent nuclear damage and is inherent in the method of treatment.