The effect of radioablation of the thyroid gland in Graves' disease with high levels of long-acting thyroid stimulator (LATS)

Abstract

Radioablation of the thyroid gland (with large doses of 131I) was attempted in thirteen carefully selected patients with Graves' disease, ophthalmopathy and (in five cases) pretibial myxedema, on the basis of previous suggestions that such therapy might ameliorate the ophthalmopathy and dermopathy. All these patients had been treated with conventional doses of 131I for their hyperthyroidism from one to eight years previously and were either euthyroid or (controlled) hypothyroid at the time of ablation. The patients were selected on the basis of persistent high titers of LATS (long-acting thyroid stimulator); the LATS and the major clinical manifestation (e.g., ophthalmopathy) had to be reasonably stable for at least one year in each patient. Because of the previous relative stability of these parameters, it was considered that each patient might act as his own control. In addition, five of these patients had circulating thyroid autoantibodies. Despite the hypothyroid status of six patients, residual thyroid parenchyma was readily demonstrable by routine means prior to attempted ablation. Complete ablation was different even with large and sometimes repeated doses of 131I. With a 1 mc. (millicurie) scanning dose, complete ablation seemed to be achieved in four patients; however with TSH (thyroid-stimulating hormone) and a 5 mc. dose, residual thyroid parenchyma was demonstrated in two of these four. In the eleven patients with such minimal residual functioning thyroid parenchyma, the twenty-four hour radioactive iodine uptake values were less than 1 per cent in each patient. Thyroxine therapy was administered to all. The longest follow-up is now two years. In none of these patients was there any significant change in the ocular manifestations or the pretibial myxedema. There were no significant changes in LATS titers. Thyroid autoanlibodies, present in five, declined in every inslance, twice to zero. Apart from the decline in thyroid auloantibodies, therefore, there has been no demonstrable effect of total or “almost total” thyroid ablation in terms of the exophthalmos, pretibial myxedema or LATS assays. The two year period may not be long enough to demonstrate that removal of the thyroid “antigen” lowers LATS titers. However the period of observation now seems long enough to suggest that removal of the thyroid “antigen” does not cause LATS to decline significantly, particularly since thyroid autoantibodies did decline significantly. If this continues to be true, either there is an antigenic stimulus for LATS in some tissue oher than the thyroid gland, or LATS arises without prior antigenic stimulation.