The interaction between growth hormone and the thyroid axis in hypopituitary patients

Abstract

SummaryAlterations in the hypothalamo-pituitary-thyroid axis have been reported following growth hormone (GH) administration in both adults and children with and without growth hormone deficiency. Reductions in serum free thyroxine (T4), increased tri-iodothyronine (T3) with or without a reduction in serum thyroid-stimulating hormone secretion have been reported following GH replacement, but there are wide inconsistencies in the literature about these perturbations. The clinical significance of these changes in thyroid function remains uncertain. Some authors report the changes are transient and revert to normal after a few months or longer. However, in adult hypopituitary patients, GH replacement has been reported to unmask central hypothyroidism biochemically in 36-47% of apparently euthyroid patients, necessitating thyroxine replacement and resulting in an attenuation of the benefit of GH replacement on quality of life in those who became biochemically hypothyroid after GH replacement. The group at highest risk are those with organic pituitary disease or multiple pituitary hormone deficiencies. It is therefore prudent to monitor thyroid function in hypopituitary patients starting GH therapy to identify those who will develop clinical and biochemical features of central hypothyroidism, thus facilitating optimal and timely replacement.

Development of additional pituitary hormone deficiencies in pediatric patients originally diagnosed with idiopathic isolated GH deficiency

“…The most frequent additional deficiency observed was TSH deficiency, which may reduce the response to GH therapy (15). Although incident hypothyroidism within the first year of GH treatment has been reported to reflect unmasking of pre-existing hypothyroidism in adult GH-deficient patients (16), the evidence in pediatric patients is more equivocal (17,18); the increasing prevalence of TSH deficiency with longer follow-up in our study is more consistent with the evolution of new deficits. The second most frequent additional pituitary hormone deficiency was LH/FSH, which occurred about one-third as frequently as TSH deficiency.…”

Low FT4 Concentrations around the Start of Recombinant Human Growth Hormone Treatment: Predictor of Congenital Structural Hypothalamic-Pituitary Abnormalities?

“…The influence of GH administration on the hypothalamic-pituitary-thyroid axis is well recognized [4]. In non-GH-deficient individuals, GH administration may result in slightly lower plasma or serum-free thyroxine (FT4) concentrations in combination with higher triiodothyronine (T3) concentrations and almost unchanged thyroid-stimulating hormone (TSH) concentrations [5][6][7].…”

Diagnosis of subclinical central hypothyroidism in patients with hypothalamic–pituitary disease by Doppler echocardiography

“…However, none of these reports assessed the echocardiographic parameters selected in our study. Notwithstanding, the interaction between GH and thyroid hormones has relevant diagnostic and therapeutic implications in patients with hypothalamic-pituitary disease (29). Accordingly, GH replacement has been shown to decrease serum FT 4 and reverse T 3 and to increase serum T 3 by improving peripheral T 4 to T 3 conversion (30).…”