[An evaluation of the incidence of hyperparathyroidism after 131I treatment for Basedow disease (Part II)].

The authors reported in a previous paper that 131I treatment for Basedow disease tends to increase in development of hyperparathyroidism (HPT) after therapy, from results showing that the measurement of levels of parathyroid hormone and calcium in the blood showed higher levels in the 131I-treated (RI) group than in the anti-thyroid drugs (ATD) group after therapy for Basedow disease. In the present work, the incidence of HPT was studied in patients with HPT that developed after treatment with 131I and/or ATD for Basedow disease at Ito Hospital. Fifteen of nineteen HPT patients had been treated with 131I and the other four had been treated with ATD. Basedow patients of the same age and sex with HPT and treated in the same year at Ito Hospital were selected as the control population for this study. The populations were 223 cases treated with 131I and 199 cases with ATD. The incidence of HPT in the RI and ATD groups was 6.7 percent and 2.0 percent, respectively. The incidence in the RI group was apparently higher than that in the ATD group. The average latent periods in the RI group and in the ATD group were 13.5 years and 4.1 years respectively. In the RI group 11 cases underwent follow-up periods of more than 10 years and 4 cases were followed up for less than 10 years. For the ATD group 3 of 4 HPT cases were followed up for less than 3 years. In the population the average follow-up periods for the RI group and the ATD group were 5.9 years and 5.3 years respectively. A relationship between radiation dose and development of HPT was demonstrated in these 15 cases of HPT. These findings suggest that 131I treatments for Basedow disease may result in development of hyperparathyroidism but the length of the follow-up period may also be an important factor in the incidence.