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

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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 εU/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 εU/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 TRH decreased after th* administration of thyroid hormone although the] were still inappropriately high in relation to th* elevated serum thyroid hormone levels. In botl the tumor and non-tumor patients, alpha subuni and TSH concentrations decreased after the administration of dexamethasone. Inthe patients with; pituitary tumor, hypophysectomy followed by radiotherapy caused a decrease in serum alpha and TSf concentrations, as well as remission of hyperthyroidism. Thepresence of elevated serum alph; concentrations and undetectable TSH-β in patientswith TSH-induced hyperthyroidism may serve to identify those patients with a pituitary tumor and in certain patients the reduction of serum alph; may better indicate the adequacyof therapy,

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