Delayed recovery of thyrotropin responsiveness after radioactive iodine therapy for hyperthyroidism

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.

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).

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.

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.