Response to TRH, serum thyroid hormone concentration, and serum markers of autoimmunity after antithyroid therapy in Graves' disease.

Abstract

In order to study the clinical significance of the TRH stimulation test the response to 200μg TRH given iv was studied in 33 patients with Graves’ disease from 3 to 70 months after discontinuation of antithyroid therapy. The relationship between the maximal increment in serum TSH and the level of thyroid hormones, the presence of circulating thyroid antibodies and the leucocyte migration inhibition, which is a measure of cellular hypersensitivity, was studied. In one group comprising 21 patients who had a normal response to TRH when tested 3 months after withdrawal of treatment or later in a few cases there was only one relapse which occurred within the first year after therapy; two patients who remained euthyroid had a temporary decrease of the response to subnormal levels (Δ TSH 30.0 mU/I) 2 1/2 and 3 years after therapy and this has remained abnormal although the patients are still euthyroid. The mean T4 and T3 and free hormone indices were significantly higher in the group of patients who had a subnormal response in comparison to the other group, although mostly the individual values were within the normal range. There was no correlation between the response and the circulating antibodies or migration inhibition. The results indicate that the TRH stimulation test has some although a limited value for the prediction of outcome after long-term antithyroid therapy. Absence of response may persist for several years without relapse and seems in some way to be related to the level of thyroid hormones in the blood, although mostly the individual values are within the normal range. No relationship exist, however, to common autoimmune parameters.