Use of lithium as an adjunct to radioiodine therapy of thyroid carcinoma.

The effect of lithium on iodine kinetics after oral 131I-iodide was studied in an athyreotic patient with follicular thyroid carcinoma. Lithium decreased the disappearance rate of 131I from the whole body and from a tumor mass in the patient's thigh from control values of 0.126/day, respectively, while having only a minimal effect on the rate of 131I disappearance from blood. The increased tumor 131I retention would be expected to increase the therapeutic:toxic ratio of 131I. However, a subsequent therapeutic dose of 131I-iodide given with lithium was accompanied by an unanticipated increase in blood 131I and, therefore, in whole body radiation, resulting in significant bone marrow depression. Although lithium may be a useful adjunct in 131I therapy of functional thyroid carcinoma, it must be used cautiously in future studies.