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

It is known that external radiation can act as a developing factor in hyperparathyroidism (HPT). To clarify whether or not 131I acts as a factor of developing HPT or not, levels of calcium and parathyroid hormone in the blood were studied in 2,954 cases of patients treated with 131I (RI group) and 530 cases treated with antithyroid drugs (ATD group). The calcium level was measured in all cases treated with 131I and/or antithyroid drugs. PTH-M (parathyroid hormone) was measured in 262 cases of the RI group and 29 cases of the ATD group which showed levels over 10 mg/dl of calcium. Fifty-eight cases (2.50%) in the RI group and three cases (1.19%) in the ATD group showed over 560 pg/ml PTH-M, which is the highest normal value. The increase in incidence of cases with over 560 pg/ml PTH-M in the RI group versus that of the ATD group is statistically significant. However, there is no statistically significant difference in the annual incidence when the follow-up period is taken into account, because the follow-up period differed between the two groups. The incidence of cases with 560 pg/ml of PTH-M was higher in the older patients than in the younger patients. These results suggest that 131I treatment for Basedow disease affects increase in the development of HPT after treatment and that the age factor is also important in the above fact.