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Am Fam Physician. 1999;60(9):2680-2682

In areas of mild to moderate iodine deficiency, multinodular goiter is a common cause of hyperthyroidism. Because antithyroid medication cannot be expected to effect a permanent cure, radiolabeled iodine 131 (131I) is a frequently chosen treatment because the suppressed extranodular thyroid is partially protected from destruction. Nygaard and associates evaluated the long-term changes in thyroid function and volume following 131I therapy for multinodular goiter.

A total of 130 patients were followed for 12 to 180 months. Sixty-six patients were pre-treated with antithyroid drugs before 131I treatment. Thyroid function variables and size of the thyroid on ultrasonography were determined before treatment, after treatment at three and six weeks, and three, six and 12 months, and thereafter once every 12 months. To reduce goiter size, more than one dose of 131I was administered to 41 patients with persistent hyperthyroidism.

The median time to euthyroidism after 131I administration was five weeks after the last treatment. Sixty-eight patients were euthyroid within three months after the first 131I treatment.

Median initial thyroid volume was 59 mL in patients receiving antithyroid pretreatment. A gradual 45 percent reduction from a median volume of 45 to 23 mL was achieved 24 months after treatment with 131I. Thereafter, no further significant thyroid volume reductions were observed. During the observation period, 11 patients became hypothyroid.

In patients who were not given antithyroid pretreatment, the median initial thyroid volume was 43 mL. A gradual 40 percent reduction 24 months after treatment with 131I was observed, after which no further significant changes occurred. Within the observation period, three patients became hypothyroid. Therefore, no significant difference was observed between patients receiving and those not receiving antithyroid pretreatment in relation to observed changes in thyroid volume after the 131I dose that cured the hyperthyroidism.

Hypothyroidism occurred significantly more often in patients pretreated with antithyroid drugs than in those who were not pretreated. Overall, hypothyroidism resulted in 14 percent of the entire group within five years. Thereafter, no further cases of hypothyroidism occurred. Analysis showed a hypothyroidism rate of 20 percent within five years in patients pretreated with antithyroid medication compared with 6 percent in patients who were not pretreated.

None of the patients had symptoms of a 131I-induced thyroiditis. In the nine patients who developed an increased thyroid volume in the first months after 131I treatment, none experienced pressure symptoms or had to undergo surgical intervention.

The results demonstrated that the most significant thyroid volume reduction occurred in the first three months after 131I treatment followed by a continuous volume-reducing effect of 131I lasting 24 months. The median thyroid volume was reduced by 43 percent. No reincrease of paranodular tissue growth was observed, indicating that the 131I treatment not only affected the hyperfunctioning nodules but also the paranodular tissue. The cumulative risk of hypothyroidism was 14 percent within five years of 131I therapy. No cases of hypothyroidism were seen beyond five years.

The authors observed cure rates of 52 percent within three months of one 131I dose in patients with multinodular toxic goiter. A total of 92 percent of the patients were cured with one or two treatments. The authors conclude that 131I should be the treatment of choice in patients with multinodular toxic goiter.

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