Antithyroid Drugs and Radioiodine and the Absence of Evidence

TO THE EDITOR: With interest we read the instructive review on the treatment of thyrotoxicosis by lagaru and McDougall (1). Therein, the authors stated that the outcome of radioiodine therapy with adjunctive methimazole or carbimazole would be equal to or better than that achieved when no antithyroid medication is administered. This statement is in compliance with the conclusion of most trials on the subject conducted over the last 60 y, including one of our trials cited in the review (2). Nevertheless, based on recent data the conclusion has to be refuted.

Recent findings from the first systematic review and metaanalysis on antithyroid drugs and radioiodine led us, unexpectedly, to the opposite conclusion (3). Indeed, all adjunctive antithyroid drugs given in the week before or after radioiodine therapy reduced the overall success. On the other hand, we found that concomitant antithyroid drugs reduced the postradioiodine exacerbation of hyperthyroidism and potentially decreased the morbidity and mortality of radioiodine therapy for hyperthyroidism. The major lesson by rebutting most previous studies including one of our own, however, was that even 6 decades of absent evidence still do not mean evidence of absent negative effects of antithyroid drugs on radioiodine treatment.

Every administration of antithyroid drugs in the week before or after radioiodine therapy will alter the overall outcome. Adequately powered trials are warranted to study the effects of longer discontinuation periods.