Elevated plasma TSH and hypothyroidism in children with hypothalamic hypopituitarism.

Basal TSH levels were found to be elevated in 6 patients with documented growth hormone deficiency and hypothyroidism. TRH (200 mug/m2 administered intravenously) led to an exaggerated TSH response. This is in contrast to the results in other GH-deficient children, with either a delayed rise of TSH (hypothalamic hypothyroidism due to TRH deficiency, n = 22), an absent TSH response (pituitary hypothyroidism due to TSH deficiency, n = 7), or a normal increase of TSH (isolated GH deficiency, n = 20). Elevated plasma TSH in the presence of hypothyroidism as seen in 6 of our patients with idiopathic hypopituitarism or craniopharyngioma, indicates an intact feedback action between the pituitary and the thyroid gland. TSH, however, seems to be inadequate for the maintenance of normal thyroid function. It is suggested that in certain patients with hypothalamic disorders, TSH is secreted in a biologically less active form.