Responses to Radioactive Iodine Therapy in Hyperthyroidism, With Special Reference to Cardiac Problems*†

THE preliminary use of radioactive iodine in the diagnosis and treatment of diseases of the thyroid (1–5) stands out as one of the major achievements in medicine in the past decade. The origins and early experience with the use of this isotope have been reviewed recently (6, 7). Continued experience with this form of therapy has enabled us to observe its advantage or disadvantage in patients with varying clinical forms of hyperthyroidism. Here we wish to present data gained from treating 330 such patients with radioactive iodine and especially in treating 47 of them who had heart disease or heart symptoms as the chief clinical manifestation of their departure from health. We seek to evaluate the usefulness of radioactive iodine in the treatment of these particular patients whose cardiac problem is the major consideration. Two objections have been raised to the use of radioactive iodine. First, that the length of time needed to control the hyperthyroidism constitutes a hazard to the patient's life; and second, that internal radiation of the thyroid causes a release of thyroid hormone and a resultant rise in the protein-bound iodine of the serum which would aggravate the existing heart disease or even precipitate thyrotoxic crisis. It has been on the basis of these fears that some physicians have given antithyroid drugs or iodide to patients soon after their therapeutic dose of radioactive iodine. We believe that this polypharmaceutical procedure has only obscured the results of the radiation therapy and as yet has yielded no precise information.