Serum thyrotropin (TSH) in pituitary and-or hypothalamic hypothyroidism: normal or elevated basal levels and paradoxical responses to thyrotropin-releasing hormone.

Abstract

ABSTRACT Using a highly sensitive and specific radioimmunoassay for thyroid-stimulating hormone (TSH), basal serum TSH levels and the response to synthetic thyrotropin-releasing hormone (TRH) were evaluated in 21 patients with unequivocal hypothyroidism resulting from pituitary or hypothalamic lesions. Baseline TSH concentrations were undetectable in only 2, being normal (n = 9) or slightly elevated (n = 10) in the rest. Three of those with elevated levels had evidence of associated primary thyroid disease. Excluding these, the mean serum TSH concentration in the remaining 18 patients (3.4 ± 0.8 (sem) μU/ml) was significantly higher (p < 0.0005) than the mean of 75 euthyroid control subjects (1.0 ± 0.1 μU/ml). Patients with hypothalamic lesions generally had higher basal TSH levels than those with pituitary lesions. Treatment with thyroxine 0.1–0.3 mg/day led to suppression of the measured TSH values. Dilutions of sera containing normal and elevated TSH levels, showed parallelism with the standard curve (...