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Radioactive iodine therapy in patients with hyperfunctioning thyroid nodules can result in hypothyroidism
The background of the study. Patients with a hyperfunctioning
thyroid nodule are often treated with radioactive iodine (I-131).
This study was done to determine the long-term effects of this therapy
on thyroid function in patients with a hyperfunctioning nodule.
How the study was done. The study group consisted of 346 patients with a hyperfunctioning thyroid nodule treated with I-131 and followed for up to 20 years. All had a thyroid nodule that concentrated I-131, and some had hyperthyroidism. After I-131 therapy, the patients were periodically evaluated for hypothyroidism.
The results of the study. There were 277 women and 69 men (mean age, 56 years). The nodule was <4 cm in diameter in 64 percent and ≥4 cm in 36 percent. Based on clinical findings, 68 percent had hyperthyroidism and 109 were normal. Factors associated with hyperthyroidism were older age and larger nodule size.
Administration of a single dose of I-131 resulted in a decrease in thyroid function to normal or below normal in 94 percent of the patients; the remaining patients required additional doses. The mean duration of follow-up was 46 months. The incidence of hypothyroidism increased progressively from 8 percent 1 year after treatment to 46 percent 10 years after treatment (Figure).
The conclusions of the study. There is a progressive increase in the frequency of hypothyroidism after I-131 therapy in patients with a hyperfunctioning thyroid nodule.
The original article. Ceccarelli C, Bencivelli
W, Vitti P, Grasso L, Pinchera A. Outcome of radioiodine-131 therapy
in hyperfunctioning thyroid nodules: a 20 years’ retrospective
study. Clin Endocrinol (Oxf) 2005;62:331-5.
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| Thyroid Digest Index | | | July 2005 Thyroid Digest |
