Serum thyrotropin responses to synthetic thyrotropin-releasing hormone in normal children and hypopituitary patients. A new test to distinguish primary releasing hormone deficiency from primary pituitary hormone deficiency.

Abstract

Synthetic thyrotropin-releasing hormone (TRH) was administered intravenously in a dose of 7 mug/kg to 20 normal children ages 4-13 yr. Serum thyroid-stimulating hormone (TSH) was measured by radioimmunoassay and rose from a mean value of 1.7 muU/ml (range = < 1.25-7.2) to a mean peak value of 21.5 muU/ml (5.2-33.2) at 15 or 30 min after administration.13 patients with idiopathic hypopituitarism and apparent normal thyroid function, ages 3-19 yr, responded to TRH in a manner very similar to the control subjects: TSH rose from a mean value of 1.8 muU/ml (range < 1.25-4.3) to a mean peak value of 18.5 muU/ml (range = 9.5-45.0) which occurred between 15 and 60 min after TRH.13 idiopathic hypopituitary patients with documented thyroid deficiency were tested after thyroid therapy had been discontinued for a minimum of 10 days. The serum TSH values in 10 of 13 patients rose from a mean base line level of 2.2 muU/ml (< 1.25-5.3) to a peak mean value of 32.5 muU/ml (9.6-61.3) between 30 and 120 min after TRH. In three patients, however, little or no TSH response was detected, even when serum thyroxine levels were extremely low. Similar to the latter group, three of five patients with hypopituitarism secondary to craniopharyngiomas had undetectable or barely measurable TSH levels before and after TRH. Two of these five patients had significant responses which were compatible with hypopituitarism resulting from damage to the hypothalamus or hypothalamic vessels instead of the pituitary. Side effects were experienced in 41 of 54 patients (76%). The effects were limited to a mild nausea-like sensation in 63% of the patients and occurred within the first 5 min after receiving TRH. No evidence of serious toxicity or long-term side effects was noted. The TRH test is a safe, effective way to measure TSH reserve in children. The positive response in 10 of 13 patients with secondary hypothyroidism supports data previously accumulated that most patients with idiopathic hypopituitarism have an abnormality of their hypothalamic-releasing hormone function, whereas the remaining minority probably have primary pituitary disease.