Regression of a large goiter in a patient with resistance to thyroid hormone by every other day treatment with triiodothyronine.

Resistance to thyroid hormone (RTH) is a syndrome of reduced responsiveness to thyroid hormone caused, in the majority of cases, by mutation in the thyroid hormone receptor (TR) beta gene. Partial compensation through increase synthesis and secretion of thyroid hormone is mediated through TSH and results in thyroid gland enlargement. Goiters are of variable size but are recalcitrant to surgical treatment, and tend to recur. We describe a 17-year-old girl with a very large goiter cosmetically unacceptable to the patient. She was the index case of a large Azorean family harbouring the TRbeta mutation R243Q. Complete goiter regression was achieved without significant side effects by administration of L-T3 every other day. The required dose of 250 microg suppressing TSH to values below 0.1 mU/L was derived by titration. Supraphysiological doses of L-T3 can be given safely as long-term treatment of goiter in patients RTH.