Hyperthyroidism and Excessive Thyrotropin Secretion

A 44-year-old woman was found to have hyperthyroidism and elevated serum thyrotropin (TSH) levels. There was no evidence of a pituitary tumor or of abnormalities in the secretion of other pituitary hormones. A modest fall in serum TSH levels and 131I uptake by the thyroid gland was observed after tri-iodothyronine administration. TSH levels increased substantially during methimazole therapy. No increases occurred after administration of thyrotropin-releasing hormone (TRH) either before or during treatment with methimazole. Administration of dexamethasone was followed by a prompt, though transient, fall in serum TSH levels. These findings suggest that the increased TSH secretion in this patient is due to excessive releasing hormone (TRH) secretion.