The TRH test in the course of treatment of hyperthyroidism

In nine patients with thyrotoxicosis (three patients with ophthalmopathy, one patient with T3 thyrotoxicosis) we followed plasma levels of triiodothyronine (T3) and thyroxine (T4) and the TRH induced TSH release before and under treatment with propythiouracil (PTU), carbimazole or methimazol. The patients were observed for 2-8 months and did not receive any thyroid hormones during this time. Before treatment the TSH responses to TRH were absent in all patients. After commencement of antithyroid drug therapy the T3 and T4 plasma values decreased to normal (T3) or subnormal levels (T4) within 1-5 weeks and the patients became euthyroid, but at that time the TRH test was still negative in all patients. Moreover, there was a lag between 2 weeks and 4 months in five of the patients before the TRH test became positive. The duration of this lag could not be correlated with any data of the history or the clinical signs. Several possible explanations for this observation are discussed. Our results suggest that the TRH-test is not suited for the control of the therapeutic effect of antithyroid drug therapy.