THYROID NODULE AUTONOMY: ITS DEMONSTRATION BY THE THYROTROPHIN RELEASING HORMONE (TRH) STIMULATION TEST

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Abstract
The response of thyrotrophin (TSH) to a single iv stimulation test with synthetic thyrotrophin releasing hormone (TRH) was compared with a thyroxine (T4)suppression test including thyroid scintiscans in 23 patients with palpable single thyroid nodules and in a control group of subjects without thyroid disease. In 16 patients with toxic adenomas and clinical hyperthyroidism no TSH-response to TRH was found as well as lack of suppression of the radioiodine uptake after T4. Thyroid scintiscans remained unchanged. Seven patients, judged to be euthyroid by clinical examination and laboratory tests, also showed no suppression by T4, as well as unchanged scintiscans. Six out of these seven patients had an absent TSH response to TRH, one had a "blunted" response. These patients were classified as having autonomously functioning thyroid adenomas. Thus there was a close correlation between absent TSH-response to TRH and non-suppressibility by T4 and it is concluded that in patients with single thyroid nodules, autonomous thyroid function can be demonstrated by the simple iv TRH stimulation test (potential hyperthyroidism or preclinical hyperthyroidism). The possibility of an altered T3/T4-secretion ratio in the development of abnormal thyroid function in thyroid adenomas is discussed. It is suggested that the rapid iv TRH stimulation test is preferable to suppression tests as a screening test for the assessment of abnormal thyroid function in patients with single thyroid nodules, providing that a reliable TSH assay method is available.

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