Ask the Doctor Irradiated Thyroid Gland

Irradiated Thyroid Gland

"Does an irradiated gland ever recover any function?" -- KF, Minneapolis, Minnesota

There are two instances when a patient who becomes hypothyroid after radioiodine may recover thyroid function, or even become hyperthyroid again.

First, shortly after radioiodine treatment, some thyroid tissue may become "stunned," and for a short period, approximately one to six weeks, the thyroid may fail to produce adequate thyroid hormone. A few months after treatment the stunned tissue may recover.

Second, over the long term, it is possible for small remnants of unaffected but abnormal thyroid tissue to grow and begin to produce sufficient thyroid hormone to allow either a reduction or elimination of the levothyroxine dose. Rarely, the growing tissue will produce recurrent hyperthyroidism.

In general, however, once thyroid tissue is destroyed by radioiodine, the hypothyroidism is permanent. And it is common for patients with Graves' disease who have normal thyroid function following treatment with radioiodine, in other words, who are euthyroid, to develop hypothyroidism at a rate of 2% to 3% each year following treatment.