Impact of lithium on efficacy of radioactive iodine therapy for Graves' disease: a cohort study on cure rate, time to cure, and frequency of increased serum thyroxine after antithyroid drug withdrawal.

Context: Radioactive iodine (RAI) is a common therapy for hyperthyroidism due to Graves' disease. A small but significant proportion of patients have recurrence of hyperthyroidism after RAI therapy. Lithium might increase RAI effectiveness by increasing RAI retention in the thyroid. However, whether lithium favorably affects the long-term outcome of RAI therapy is still a matter of argument.
Objective: The objective of the study was to compare the efficacy of RAI given with or without concomitant lithium treatment.
Design: This was a retrospective cohort study.
Setting: The study was conducted at a tertiary university center.
Patients: Six hundred fifty-one patients with newly diagnosed Graves' disease participated in the study.
Intervention: Two hundred ninety-eight patients were treated with RAI plus lithium (900 mg/d for 12 d) and 353 with RAI alone.
Main Outcome Measures: Proportion of cured patients and time to achieve cure of hyperthyroidism during 1 yr of follow-up was measured.
Results: PATIENTS treated with RAI plus lithium had a higher cure rate (91.0%) than those treated with RAI alone (85.0%, P = 0.030). In addition, patients treated with RAI plus lithium were cured more rapidly (median 60 d) than those treated with RAI alone (median 90 d, P = 0.000). Treatment with lithium prevented the serum free T(4) increase after methimazole withdrawal and RAI therapy. Side effects after RAI therapy occurred in a subset of patients and were mild, transient, and without differences in the two groups.
Conclusions: RAI combined with lithium is safe and more effective than RAI alone in the cure of hyperthyroidism due to Graves' disease.