THERAPEUTIC EFFECTS FROM REPEATED DIAGNOSTIC DOSES OF I¹³¹IN ADULT AND JUVENILE HYPERTHYROIDISM*†

Abstract

TRACER methods with small doses of radioiodine, I131, are commonly used in hyperthyroidism to follow the course of the disease under the influence of a particular therapy. It is generally assumed that these small amounts of isotope in themselves have no physiologic effect. Evidence obtained in this clinic from three directions has indicated that this assumption may not be correct. First, it has been shown that some patients with hyperthyroidism are unusually sensitive to radiation effect from therapeutic doses of I131 (1). This suggests that smaller doses of isotope also may evoke a response. Second, it has been found in one clinic that an occasional remission from thyrotoxicosis may follow ACTH administration (2, 3), whereas this response has not been noted in another clinic (4). The only apparent difference which can be demonstrated between the two investigations is in the use of diagnostic tracer methods with I131. Larger and more frequently repeated doses of I131 have been administered in the former compared to the latter. Third, it has been a source of some speculation as to why occasional patients with hyperthyroidism claim to feel better after a single diagnostic tracer test. It is questionable whether a factor of suggestion is the only reason.