Immunological effects of Graves' disease therapy

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

Has the use of antithyroid drugs for Graves' disease become obsolete?

In spite of an experience of almost 50 years of use of antithyroid drugs and radioiodine for the treatment of Graves' disease, the rationale for choice is often obscure. Early reports of high remission rates during thiourea therapy were followed by less optimistic ones, which along with other factors may have fueled the current major shift toward use of radioiodine. This review examines whether or not the use of antithyroid drugs indeed may have become obsolete. The intrathyroidal and extrathyroidal mechanisms of action of the drugs are reviewed with emphasis on their potential immunosuppressive effects. The latter may involve a direct effect on thyroid follicular cells, a direct suppression of TSH receptor antibody formation, or indirect effects mediated via heat shock proteins, oxygen free radicals, and the immune system. Potential factors associated with success or failure with antithyroid drug therapy are discussed, such as the effects of dose and duration of treatment, iodine milieu, and concomitant L-thyroxine therapy. The risks inherent to radioiodine therapy are only briefly described with emphasis on the possible aggravation by radioiodine of preexistent ophthalmopathy. The reader must decide whether the evidence marshalled convincingly indicates that the use of the thiourea compounds should be abandoned. The author thinks not, and is optimistic that imminent discovery of the yet elusive and enigmatic pathogenesis of Graves' disease will permit new and innovative treatment or more effective use of currently available therapies.