Pituitary resistance to thyroid hormone action with preserved circadian rhythm of thyrotropin in a postmenopausal woman.

We assessed the 24-h behavior of circulating TSH and the dopaminergic control on TSH release in a postmenopausal woman, who had elevated levels of serum thyroid hormones and an inappropriately high concentration of serum TSH, indicating pituitary resistance to thyroid hormone action. The patient was found to have a daily profile of serum TSH similar to that of normal subjects, except for the persistently elevated 24 h levels, suggesting that alterations in thyroid hormone negative feedback control did not affect substantially circadian TSH rhythm. The acute administration of a dopamine antagonist drug (metoclopramide) resulted in a markedly elevated peak of serum TSH, similar both in the morning and in the evening. The chronic administration of a dopamine agonist drug (bromocriptine) reduced basal and TRH-stimulated TSH, restored circadian TSH variations to lower levels, and normalized other thyroid function tests. Although the metoclopramide test results confirmed the existence of an increased dopaminergic inhibitory tone in nonneoplastic inappropriate secretion of TSH, the outcome of bromocriptine treatment indicated that the dopaminergic control over TSH release was not enough in this case of PRTH.