Endocrine Abstracts

Introduction: Radioactive Iodine (RAI) is a well-established and effective treatment for hyperthyroidism. Lithium (Li) blocks the release of organic iodide and thyroid hormone from the thyroid gland without effecting thyroidal RAI uptake. Through decreasing the loss of RAI from the thyroid it has also been shown to reduce urinary RAI excretion. Its use as an adjunct to RAI in the therapy of hyperthyroidism has been postulated, but information on the subject is limited.

Objective: To evaluate the efficacy of RAI therapy alone and RAI combined with lithium for treatment of hyperthyroidism.

Methods: 41 patients with hyperthyroidism were randomly assigned to treatment with RAI (controls) or RAI plus lithium and evaluated for changes in thyroid function on the day and weeks 1, 3, 9, 12 and at least 6 months post treatment. Urinary Iodine (UI) excretion measurements from 24-hour urine collections of 29 trial patients (14 Li vs 15 Non-Li) were obtained at −7, 0 and +7 days from RAI therapy.

Results: Both groups were similar in age, sex and received equivalent mean doses of RAI. One of 22 patients treated with RAI plus lithium (4.5%) and 2 of 19 patients treated with RAI alone (10.5%) were not cured (euthyroid + hypothyroid) (P=ns). UI excretion levels overall (Li + Non-Li) increased one-week post RAI (152 nmol/mmol) compared to levels measured immediately before RAI (52 nmol/mmol) (P=<0.001). There was no significant difference in UI excretion in the Li vs Non-Li group (P=ns).

Conclusions: Lithium does not appear to improve the efficacy of RAI and hence is not translating into an improved outcome for patients. Lack of a significant difference might be due to the excellent cure rate achieved in both groups during this trial. A more definitive conclusion will be reached upon greater patient recruitment and completion of the continuing trial.