Serum thyrotrophin in patients with destructive pituitary lesions assessed by a sensitive immunoradiometric assay

Using a sensitive immunoradiometric assay, serum concentrations of thyrotrophin (TSH) were measured both basally and after intravenous thyrotrophin releasing hormone (TRH) in two groups of patients with destructive pituitary lesions. Group A patients, who had more extensive pituitary hormone deficiencies and biochemical evidence of hypothyroidism at the time of study, had significantly lower mean serum TSH concentrations than the group B patients who were biochemically euthyroid. Basal TSH was below the lowest value seen in a control group of normal subjects in 5 of the 8 group A patients. In all patients TSH increased significantly after injection of TRH; the peak values being significantly correlated with the basal. In contrast to recent studies, which have emphasised other mechanisms in the production of secondary hypothyroidism, our data suggest that inadequate production of immunoassayable TSH is a common cause of secondary hypothyroidism in patients with destructive pituitary disease. Little, if any, additional clinical information is to be gained by measurement of TSH after TRH stimulation in this circumstance.