A long-term follow-up study of late-onset hypothyroidism and prognosis of hyperthyroid patients treated with radioiodine

We performed a follow-up study of 7,325 cases of hyperthyroidism treated with radioiodine in Japan from 1953 to 1967. Of these cases, there were 1,892 which clearly had or had not received thyroid hormone substitution therapy. Based on this, the frequency, period of onset and background of patients with hypothyroidism were investigated. There was a high incidence of cases among women in their thirties who had received large doses of radioiodine. Also, consistent with previous reports, a continuous, long-term increase in hypothyroidism was recognized. There is a need to investigate the course of the disease more throughly. The outbreak of thyroid tumors was also investigated. No clear increase in the incidence of tumors was seen in cases that had received radioiodine therapy. An evaluation of prognosis was made to establish the anticipated mortality rate using the mortality rate of the population at large as a base for comparison. In the 2,379 cases in which there was an effective response, no significant increase in either mortality or cancer mortality was recognized in the group that received radioiodine therapy. Nor was there an increase in the mortality rate among the younger patients in the treated group. Although there was a tendency for the overall mortality to increase when large quantities of radioiodine were prescribed. There is, however, some uncertainty as to whether or not there is a direct relationship to hypothyroidism. From this standpoint, rigorous observation during the course of treatment is important as well as commencement of appropriate substitution therapy. (author)