Controversies in radioiodine therapy: relation to ophthalmopathy, the possible radioprotective effect of antithyroid drugs, and use in large goitres

Abstract

In routine use for more than 50 years, radioiodine ( 131 I) is generally considered safe and devoid of major side effects. Therefore, it is surprising that relatively many aspects of radioiodine therapy are controversial, as illustrated by recent international questionnaire studies. Our review aims at highlighting three of these areas -namely, the influence of 131 I on the course of Graves' ophthalmopathy, the possible radioprotective effects of antithyroid drugs, and the use of 131 I in large goitres. 131 I therapy carries a small (but definite) risk of causing progression of Graves' ophthalmopathy. Identification of risk factors (thyroid dysfunction, high level of thyroid-stimulating hormone (TSH) receptor antibodies, cigarette smoking) allows the identification of patients at risk and the institution of concomitant glucocorticoid treatment, thereby hindering progression of eye disease.On the basis, largely, of retrospective data, it appears that carbimazole (or methimazole), if stopped 3-5 days before treatment, does not influence the outcome of 131 I therapy. Simultaneous thyrostatic medication most probably reduces the efficacy of 131 I, as does restarting it within 7 days. Propylthiouracil seems to have a more prolonged radioprotective effect than carbimazole.Surgery is the treatment of first choice in patients with a large goitre. However, in the case of patient ineligibility or preference, 131 I therapy may be an option. The treatment has a favourable effect on tracheal compression and inspiratorycapacity, but the reduction in thyroid volume is only 30-40%. Inpatient treatment, necessitated by the large doses, makes the treatment cumbersome.Controversy related to radioiodine therapy is mainly based on the lack of adequate prospective randomised studies comparing efficacy, side effects, cost and patient satisfaction.

Remission of Graves’ disease during anti-thyroid drug therapy. Time to reconsider the mechanism?

“…Once that cycle is broken by making the patient euthyroid by one or the other drug or by surgery, most patients will gradually experience remission of the disease. Euthyroidism caused by radioiodine destruction of the thyroid gland is different, because radioiodine therapy has a particular direct effect on thyroid autoimmunity (16).…”

The effects of recombinant human thyrotropin, in normal subjects and patients with goitre

“…Using the same dose of 131 I, the goitre size reduction seems to be amplified from approximately 40 to 60% within a year, if rhTSH prestimulation is applied. This may lead to more satisfactory results of 131 I therapy in patients with very large goitres, in whom thyroidectomy usually is the favoured treatment option (Bonnema et al, 2000(Bonnema et al, , 2002a(Bonnema et al, , 2002bHegedüs et al, 2003).…”

Efeito do propiltiouracil sobre a eficácia da dose terapêutica de iodo radioativo (I-131) no hipertiroidismo por doença de graves

“…(32). Em relação ao MMI, este parece não ter influência sobre o resultado da dose terapêutica quando suspenso 4 dias antes da DT (5,17,29,30). Nossa análise é compatível com esses dados, já que houve similaridade de curados e não curados entre o grupo do MMI e o grupo sem AT pré-DT (figura 1).…”

“…Com relação ao PTU, seu efeito radioprotetor é sugerido há mais de 30 anos, com trabalhos mais recentes mostrando os mesmos resultados (5,16,18,31,32). Santos e cols.…”