The occurrence of hypothyroidism following radioactive iodine treatment of toxic nodular goiter is related to the TSH level.

BACKGROUND: Strategies to increase frequency of euthyroidism following radioactive (RAI) treatment of hyperthyroidism are required.

AIMS: To examine the role of TSH in development of hypothyroidism post RAI treatment in patients with Graves' disease (N = 98) or toxic nodular goiter, TNG (N = 88).

DESIGN: This retrospective study examined thyroid status over a mean of 3.7 years post-RAI.

RESULTS: Although RAI dose was significantly higher in TNG group, hypothyroidism occurred more frequently in Graves' disease (71.4 and 22.7%) P < 0.001. The TSH levels at the time of RAI treatment were lower in TNG patients who remained euthyroid, (0.4+/-0.1 vs. 1.2+/-0.5 mU/l, P < 0.0022).

CONCLUSIONS: A higher frequency of euthyroidism occurs in patients with TNG than with Graves' disease following RAI, particularly when suppressed TSH levels were suppressed at time of RAI-treatment.