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Graves’ disease with hyperthyroidism occasionally occurs after radioactive iodine therapy for nodular goiter
The
background of the study. Patients with nodular goiter may be
treated with radioactive iodine (I-131) to decrease thyroid function or
goiter size. However, this treatment may result in immunogenic hyperthyroidism
(hyperthyroidism caused by Graves’ disease). In this study, the
frequency of the appearance of thyrotropin (TSH)-receptor antibodies (TSHR-Ab)
characteristic of Graves’ hyperthyroidism was determined in a large
group of patients with goiter treated with I-131.
How the study was done. The study subjects were 999 patients with a nodular goiter or a diffuse (nonimmunogenic but autonomous [TSH-independent]) goiter who were treated with a high dose of I-131 because they had overt hyperthyroidism or subclinical hyperthyroidism (serum thyrotropin [TSH] concentration, ≤0.1 mU/L). The goals of I-131 therapy were to eliminate hyperthyroidism and the autonomously functioning thyroid tissue and to decrease goiter size.
Serum TSH, free T4, and TSHR-Ab were measured and thyroid ultrasonography and nuclear scanning were performed before and after I-131 therapy. Post-radioiodine Graves’ hyperthyroidism was defined as overt clinical and biochemical hyperthyroidism, a high serum TSHR-Ab concentration, the appearance of hypoechogenicity on ultrasonography, and a homogeneous pattern of uptake on nuclear scan.
The results of the study. Fifteen of the 999 patients (1.5 percent) had Graves’ hyperthyroidism after I-131 therapy. All 15 patients had overt hyperthyroidism with hypoechogenicity on ultrasonography, homogeneous uptake on nuclear scan, and high serum TSHR-Ab concentrations; 1 patient had Graves’ eye disease. The hyperthyroidism occurred an average of 5 months after I-131 therapy.
Thirteen of the 999 patients (1.3 percent) had a transient rise in serum TSHR-Ab concentration, but not hyperthyroidism, after I-131 therapy.
The conclusions of the study. Patients with autonomous thyroid function caused by nodular or diffuse goiter have a low risk of Graves’ hyperthyroidism after I-131 therapy.
The original article. Schmidt M, Gorbauch E, Dietlein M, Faust M, Stutzer H, Eschner W, Theissen P, Schicha H. Incidence of postradioiodine immunogenic hyperthyroidism/Graves’ disease in relation to a temporary increase in thyrotropin receptor antibodies after radioiodine therapy for autonomous thyroid disease. Thyroid 2006;16:281-8.
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