Alterations in thyroid I-131 uptake, basal metabolic rate and serum cholesterol following treatment of hyperthyroidisim with radioactive iodine: Value in early prediction of success or failure of therapy

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Sixty-six hyperthyroid patients given eightynine therapeutic doses of radioiodine were evaluated before and serially after therapy in regard to clinical status, thyroid uptake, basal metabolic rate, serum cholesterol and proteinbound iodine as determined chemically. Three groups of patients—those showing failure, remission and myxedema—were distinguished by clinical criteria after adequate follow-up (average of twenty-one, seventy-seven and seventy-nine weeks, respectively). Differences in clinical severity were evident prior to treatment. Approximately two-thirds of the failure, one-third of the remission, and one-seventh of the myxedema groups were severely hyperthyroid initially. The basal metabolic rate was the only test differentiating significantly all three groups before treatment. The response groups were clearly distinguishable by the thyroid uptake as early as six to nine weeks following therapy and at each period of observation thereafter. The basal metabolic rate was almost as effective and the cholesterol somewhat less effective in differentiating failures from remissions. Though based upon very small samples, the protein-bound iodine appeared at least as effective as the basal metabolic rate. With one exception a combination of the variables was more effective than any single measure in separating the three groups at every time interval after therapy. Ninety-six per cent of those who were hyperthyroid clinically and whose uptake and basal metabolic rate were both either abnormally high or borderline at their first adequate posttherapy evaluation proved eventually to be treatment failures. Six of ten who were hyperthyroid clinically, but with either uptake or basal metabolic rate definitely normal, were treatment failures. Only 2 per cent of those who were (1) hyperthyroid clinically with uptake and basal metabolic rate both definitely normal, or (2) probably euthyroid clinically with either uptake or basal metabolic rate normal, or (3) definitely euthyroid clinically, were failures. The serum cholesterol was chiefly of corroborative value. As early as six to nine weeks, over one-half of the patients in the remission and myxedema groups but only one-twentieth of those in the failure group had non-palpable glands. At later intervals the group differences were even more striking.