Incidence of hypothyroidism after radioactive iodine therapy for thyrotoxicosis in Hong Kong Chinese

Abstract

The incidence of hypothyroidism in 1396 Chinese patients in Hong Kong treated for hyperthyroidism with 131I therapy is presented using the life-table method of analysis. One year after therapy only 6% of patients were hypothyroid, but the subsequent annual incidence was 3.5%, emphasizing the need for life-time surveillance of these patients. A higher incidence of subsequent hypothyroidism was found in patients with diffuse compared with nodular glands and small (less than 40 g) compared with larger glands. Previous medical or surgical treatment, the total dose or number of doses of 131I, the severity of thyrotoxicosis and the age of the patient did not influence the rate of onset of hypothyroidism. The data suggest that in order to minimize the occurrence of hypothyroidism a lower dose of 131I per gram of thyroid mass should be used for patients with small diffuse glands.