The size of sporadic nontoxic goitres is reduced on average by 50% after a single dose of 4.77 MBq 131I/g thyroid. Independent determinants of the relative decrease in thyroid volume are administered 131I dose and initial goitre size. Nonresponders (14%) and those with late recurrence of goitre growth (8%) have larger goitres and more often dominant nodules than responders. Determinants of postradioiodine hypothyroidism (cumulative risk 58% after 8 years) are the presence of TPO antibodies, a family history of thyroid disease and a relatively small goitre. The implications of these findings are that the efficacy of a given 131I dose can be enhanced when administered at an earlier stage when the goitre is still smaller, albeit at the expense of an increased risk for developing hypothyroidism.

A randomized clinical trial was performed in consecutive patients with sporadic nontoxic nodular goiter to compare efficacy and side effects of iodine-131 ((131)I) therapy with suppressive levothyroxine (L-thyroxine) treatment. Sixty-four patients were randomized after stratification for sex and menopausal age to receive (131)I (4.44 MBq/g thyroid; group A) or suppressive L-thyroxine treatment aiming at TSH values between 0.01 and 0.1 mU/L (group B). The main outcome measurements after 2 yr were goiter size by ultrasound, serum thyroid function tests, markers of bone turnover, and bone mineral density (BMD). Fifty-seven patients completed the trial. Goiter size was reduced after 2 yr by 44% in group A and by 1% in group B (P< 0.001). Nonresponders (goiter reduction <13%) were 1 of 29 patients in group A and 16 of 28 patients in group B (P = 0.00001). In responders, goiter reduction in group A (46%) was greater than in group B (22%; P< 0.005). In group A, 45% of patients developed hypothyroidism. In group B, 10 patients experienced thyrotoxic symptoms, requiring discontinuation of treatment in 2 (in 1 because of atrial fibrillation). Markers of bone formation and bone resorption increased significantly in group B, related to a mean decrease of 3.6% of BMD at the lumbar spine after 2 yr (from 1.09 +/- 0.22 to 1.05 +/- 0.23 g/cm(2); P< 0.001), both in pre- and postmenopausal women. No changes in BMD were observed in group A. In conclusion, (131)I therapy is more effective and better tolerated than L-thyroxine treatment in patients with sporadic nontoxic goiter. Suppressive L-thyroxine treatment results in significant bone loss.

A randomized clinical trial was performed in consecutive patients with sporadic nontoxic nodular goiter to compare efficacy and side effects of iodine-131 ((131)I) therapy with suppressive levothyroxine (L-thyroxine) treatment. Sixty-four patients were randomized after stratification for sex and menopausal age to receive (131)I (4.44 MBq/g thyroid; group A) or suppressive L-thyroxine treatment aiming at TSH values between 0.01 and 0.1 mU/L (group B). The main outcome measurements after 2 yr were goiter size by ultrasound, serum thyroid function tests, markers of bone turnover, and bone mineral density (BMD). Fifty-seven patients completed the trial. Goiter size was reduced after 2 yr by 44% in group A and by 1% in group B (P< 0.001). Nonresponders (goiter reduction <13%) were 1 of 29 patients in group A and 16 of 28 patients in group B (P = 0.00001). In responders, goiter reduction in group A (46%) was greater than in group B (22%; P< 0.005). In group A, 45% of patients developed hypothyroidism. In group B, 10 patients experienced thyrotoxic symptoms, requiring discontinuation of treatment in 2 (in 1 because of atrial fibrillation). Markers of bone formation and bone resorption increased significantly in group B, related to a mean decrease of 3.6% of BMD at the lumbar spine after 2 yr (from 1.09 +/- 0.22 to 1.05 +/- 0.23 g/cm(2); P< 0.001), both in pre- and postmenopausal women. No changes in BMD were observed in group A. In conclusion, (131)I therapy is more effective and better tolerated than L-thyroxine treatment in patients with sporadic nontoxic goiter. Suppressive L-thyroxine treatment results in significant bone loss.

In healthy adults, lean body mass rather than body weight explains the differences in thyroid volume between males and females and between obese and non-obese subjects. Lean body mass appears to be a major determinant of thyroid size.

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