Delayed recovery of thyrotropin responsiveness after radioactive iodine therapy for hyperthyroidism

BACKGROUND: After radioactive iodine therapy for hyperthyroidism, an expected lag in the responsiveness of thyrotropin (TSH) is 60 to 90 days. In our experience, however, many patients seemed to have a more prolonged lag in TSH recovery. METHODS: A retrospective chart review was performed in 58 patients who underwent radioactive iodine therapy for hyperthyroidism (52 with Graves disease, 5 with toxic nodular goiters, and 1 with a toxic adenoma). RESULTS: Forty-nine patients (84%) had appropriate responses of TSH for their level of serum thyroid hormone. Thirty-one became hypothyroid, 12 became euthyroid, and 6 remained hyperthyroid. Nine patients (16%) had a lag in their TSH responsiveness. The TSH remained low for 3 months in 5 patients, for 9 months in 3 patients, and 1 patient had low levels of serum TSH for at least 12 months. CONCLUSIONS: After radioactive iodine therapy for hyperthyroidism, decisions upon further therapy must be based upon the clinical status as well as the serum levels of TSH and thyroid hormones.