Evaluation of plasma thyrotrophin response to thyrotrophin releasing hormone in Graves' disease and in hyperactive thyroid adenoma before and after treatment

The effects of thyrotrophin releasing hormone (TRH) on plasma thyrotrophin (HTSH) were studied in patients with thyroid disorders. TRH was given either i.v. (200 or 600 μg) or by mouth (20 mg). No definite increase in plasma HTSH after TRH occurred in 35 thyrotoxic patients (28 with Graves' disease, 6 with toxic adenoma and 1 with a hypothalamic pituitary vascular tumour and high basal plasma HTSH). 4 out of 5 patients with hyperactive adenoma without thyrotoxicosis were also TRH unresponsive, while in the fifth subject, in whom the functional suppression of the normal thyroid tissue was not complete, a normal response was found. 4 out of 5 patients with non thyrotoxic ophthalmic Graves' disease did not respond to TRH. 23 subjects were studied after treatment of thyrotoxic Graves' disease, either with methimazole (14 cases) or with ¹³¹I (9 cases): out of 14 euthyroid patients, 6 had undetectable basal plasma HTSH, 6 had values in the normal range and 2 had elevated levels. Only 7 subjects showed a response to TRH (normal in 3 cases, exaggerated in 2 and impaired in 2). Out of 9 hypothyroid patients, 1 had undetectable basal plasma HTSH, 1 a normal value and 7 had elevated levels. 7 subjects were TRH responsive (normal increase in 2 cases, exaggerated in 4, impaired in 1). 2 patients were studied after surgery for toxic adenoma: 1 was hypothyroid with high basal plasma HTSH and gave an exaggerated response to TRH, while the other was euthyroid and had normal basal plasma HTSH which did not increase after TRH. The T ₃ suppression test was performed in the patients with ophthalmic Graves' disease and in 6 subjects after treatment of thyrotoxic Graves' disease: an abnormal T ₃ suppression test coincided with TRH unresponsiveness in all cases but one.