Thyrotropin-Induced Hyperthyroidism: Use of Alpha and Beta Subunit Levels to Identify Patients with Pituitary Tumors

Abstract

Six hyperthyroid patients with inappropriately elevated serum thyrotropin (TSH) had serum concentrations of the common alpha subunit of the glycoprotein hormones (alpha) and the beta subunit of TSH (TSH-β) measured by radioimmunoassay. The three patients with a pituitary tumor had markedly elevated serum alpha levels of 105, 16.6, and 19.5 ng/ml and TSH of 34, 1.7, and 5.6 eU/ml, yielding molar alpha to TSH ratios of 31 to 98; TSH-β was not detected (<;0.5 ng/ml). The three patients without a pituitary tumor had serum alpha concentrations of 1.2, 0.5, and 1.0 ng/ml and serum TSH levels of 160, 9.3, and 90 eU/ml, yielding molar alpha to TSH ratios <1; TSH-β was 1.3, 0.5, and 0.5 ng/ml. Subunit and TSH secretion in the patients with a pituitary tumor demonstrated little or no change after thyrotropin releasing hormone (TRH) or thyroid hormone administration. In contrast, serum subunit and TSH levels increased after TRH in the patients withou a pituitary tumor; both basal and peak subuni and TSH levels after...