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Letter to the editor |
Department of Endocrinology and Metabolism, Odense University Hospital, DK-5000 Odense C, Denmark
Address correspondence to: Steen J. Bonnema, M.D., Ph.D., Department of Endocrinology and Metabolism, Odense University Hospital, DK-5000 Odense C, Denmark. E-mail: steen.bonnema{at}ouh.fyns-amt.dk.
To the editor:
We thank Bartalena et al. (1) for their comment. The main purpose of our study (2) was to clarify whether propylthiouracil impairs the efficacy of radioiodine therapy in hyperthyroid diseases. It may be true that this feature of propylthiouracil is unique among the antithyroid drugs available, perhaps due to the larger doses of propylthiouracil needed to control the hyperthyroidism. We fully agree with Bartalena et al. that untreated hyperthyroidism may have serious health consequences. The risk of developing heart arrhythmias and osteoporosis are well known. However, it is not elucidated by large controlled studies whether hyperthyroidism results in irreversible physical or mental impairment despite attainment of euthyroidism. Nevertheless, we believe, probably in agreement with most other physicians, that euthyroidism should be obtained as soon as possible when overt hyperthyroidism is detected. Treatment of hyperthyroidism can be achieved by antithyroid drugs, radioiodine, or surgery. Obviously, total thyroidectomy with subsequent L-thyroxine substitution is a very quick way to restore euthyroidism, but this method is rarely the first choice (3). Therefore, the choice initially stands between antithyroid drugs and radioiodine. A head-to-head comparison between these two methods including an evaluation of patient satisfaction and the long-term performance has not been conducted, but indeed this would be relevant. According to surveys (3) performed in the early 1990s, physicians do not agree on the primary therapy of choice. It is evident that both antithyroid drugs and radioiodine are useful for controlling hyperthyroidism, but the time interval until euthyroidism is obtained is most variable due to differences in the individual susceptibility to the treatment. The advantages of using an antithyroid drug are clear: it is simple and cheap, easily initiated, and the impact on the thyroid gland is reversible. On the other hand, side effects may occur, and recurrence of hyperthyroidism is encountered in a significant part of the patients after withdrawal of the drug. In addition, if radioiodine subsequently is given, the cure rate may be reduced by using an antithyroid drug pretreatment. Results in this area have been conflicting, but based on recent randomized trials methimazole (4, 5) seems neutral in this setting, whereas propylthiouracil has a detrimental effect (2). Radioiodine results in definite cure of the disease (often including permanent thyroid failure), but the success rate is correlated to the thyroid dose, and a second radioiodine therapy may be needed. It has not been settled by a randomized trial whether an antithyroid drug or radioiodine is most effective in terms of the shortest time interval to obtain euthyroidism. Other important issues in this context are side effects and patient satisfaction. At present, the choice between antithyroid drugs and radioiodine is based on individual factors, including patient preference and local traditions.
We agree with Bartalena et al. (1) that overtly hyperthyroid patients should not go untreated. Therefore, as discussed in our paper (2), there is no doubt that patients should be offered an antithyroid drug, if rapid access to radioiodine is impossible. If radioiodine is given to untreated hyperthyroid patients, the risk of a radioiodine-induced hyperthyroid crisis is very low. In fact, the thyroid hormone levels steadily decline after radioiodine therapy of hyperthyroid patients (2, 6, 7). In the studies by Burch et al. (6) and Andrade et al. (7), the thyroid function was closely monitored after radioiodine administration. Nevertheless, we agree that the risk of a hyperthyroid exacerbation should be minimized, particularly in elderly patients or in cases with known cardiovascular heart diseases. Such patients should preferably be pretreated with antithyroid drugs before radioiodine. The thyroid function after radioiodine may also show a highly variable and unpredictable course, and the patients should therefore be monitored relatively closely in this period. If the antithyroid drug is discontinued before radioiodine administration, a transient hyperthyroid relapse follows the treatment (2, 6). We recognize that use of lithium in conjunction with radioiodine may be beneficial in this setting (8), as outlined by Bartalena et al. (1). Although lithium seems to increase the thyroid iodine retention, the final cure rate is not increased by the adjuvant use of lithium 900 mg/d for 3 wk, as demonstrated by a large randomized study (9). We do not use lithium, but we recommend that the antithyroid drug, used initially to render the patient euthyroid, is paused 4 d before and resumed 1 wk after radioiodine, with final discontinuation of the drug if euthyroidism is verified 1 month later. We have recently proved by a randomized trial (10) that such an approach, using methimazole, results in a stable euthyroid state throughout this early period after radioiodine and without adversely affecting the final outcome.
The ideal management of hyperthyroid disorders as well as the most favorable radioiodine regimen still remains to be established. Indeed, recognizing that lack of consensus prevails among centers handling thyroid disorders, future well-designed studies should address these issues.
Received November 8, 2004.
References
This article has been cited by other articles:
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  S. J. Bonnema and L. Hegedus Authors' Response: Treatment with Thionamides before Radioiodine Therapy for Hyperthyroidism: Yes or No? J. Clin. Endocrinol. Metab., February 1, 2005; 90(2): 1256 - 1257. [Full Text] [PDF]
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