Course of thyroid iodine concentration during treatment of endemic goitre with iodine and a combination of iodine and levothyroxine

Abstract

In the treatment of endemic goitre, the concept of giving levothyroxine in combination with iodine offers a promising therapeutic approach by influencing not only TSH secretion but also intrathyroidal iodine content. However, little is known about the doses of iodine necessary to correct intrathyroidal iodine deficiency. To get more information on this important issue, we conducted a prospective, double-blind study on the effect of a monotherapy with 500 micrograms iodide/day and a combined treatment with 100 micrograms levothyroxine and 100 micrograms iodide/day on thyroid iodine concentration as measured by fluorescence scintigraphy. In a group of 12 patients, a 4-month treatment with 100 micrograms levothyroxine and 100 micrograms iodide/day did not significantly affect thyroid iodine concentration (0.35 +/- 0.14 vs 0.37 +/- 0.11 mg/g). The application of 500 micrograms iodide/day in these patients during a second 4-month period resulted in a sharp increase in thyroid iodine concentration from 0.37 +/- 0.11 to 0.61 +/- 0.14 mg/g (p less than 0.01). Another group of 8 patients first treated with 500 micrograms iodide/day also showed a significant increase in iodine concentration from 0.35 +/- 0.14 to 0.65 +/- 0.20 mg/g (p less than 0.01). After switching to the combination regimen during a second 4-month period, thyroid iodine concentration slightly decreased, particularly in those patients with high iodine concentrations after monotherapy with iodide (0.65 +/- 0.20 vs 0.50 +/- 0.12 mg/g, p less than 0.05). In conclusion, treatment with 500 micrograms iodide/day could sharply increase thyroid iodine concentration in patients with endemic goitre. In contrast, a combination of 100 micrograms levothyroxine and 100 micrograms iodide/day had no significant effect on thyroid iodine concentration.