Beneficial effects of adequate iodine supply on characteristics of thyroid autonomy

Abstract

Our aim was to establish the characteristics of thyroid autonomy (TA) in Slovenian patients and the required therapeutic dose of radioiodine before and ten years after the increase in mandatory salt iodization from previous 10 mg of potassium iodide to 25 mg per kg in 1999 because almost no data about TA and radioiodine treatment with respect to iodine supply are available. Retrospective clinical study. We reviewed records of all patients referred for the first time in 1998 and 2009 to the Thyroid Department at the University Medical Centre Ljubljana which is a tertiary referral centre with a stable catchment area for more than 20 years. TA was diagnosed by thyroid function, ultrasound, scintigraphy and negative TSH receptor antibodies. Demographic characteristics and the applied dose of radioiodine were evaluated. In 1998, significantly more patients presented with TA than in 2009 (383 of 3243, 11·8% and 333 of 4546, 7·3%, respectively, P < 0·001). In 1998, the ratio between hyperthyroid and euthyroid patients was higher than in 2009 (6:1 and 2·1:1, respectively, P < 0·001). In 1998, patients were younger than in 2009 (mean 63·8 ± 13·9 and 66·8 ± 14·9 years, respectively, P < 0·004). Hyperthyroid patients were older than euthyroid in both years (P < 0·001). In 1998, mean applied dose of radioiodine was significantly lower than in 2009 (713 ± 306 and 791 ± 194 MBq, respectively, P = 0·003). In adequate iodine supply, TA is less frequent, patients are less often hyperthyroid, they are older and cured with higher doses of radioiodine than in mild iodine deficiency.