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Growth hormone therapy can cause central hypothyroidism in patients with hypopituitarism
The background of the study. Treatment of patients with pituitary disease with growth hormone (GH) may result in decreases in serum thyroxine (T4) or thyrotropin (TSH) concentrations. This study determined the frequency of changes in pituitary–thyroid function in a large group of adults with pituitary disease during GH treatment.
How the study was done. The study subjects were 243 patients with GH deficiency caused by a pituitary tumor, brain tumor, or other pituitary disorder; 179 had been treated surgically and 171 with radiation therapy. At base line, 159 patients (65 percent) had hypothyroidism due to their pituitary disease (central hypothyroidism) and 84 (35 percent) did not. The patients were treated with GH, and their thyroid function was assessed periodically after the initiation of GH therapy. At three and six months, a diagnosis of hypothyroidism was made if the patient’s serum T4 values were low and serum TSH was low or normal.
The results of the study. In the 84 patients who did not have central hypothyroidism and were not taking T4 at base line (untreated group), the serum T4 values decreased slightly at three months, whereas serum TSH values did not change. The serum T4 value was low at three months in 25 (30 percent) of these patients, and therefore they were treated with T4. In the remaining 59 patients, the mean serum T4 values were slightly lower at six months, and 5 (6 percent) had hypothyroidism. Overall, 30 patients (36 percent) had hypothyroidism during the first six months of GH therapy.
In the T4-treated group, the mean serum T4 value decreased slightly at three months, but there were no changes in serum TSH values (the latter were undetectable at all times). The serum T4 values decreased to below normal in 23 patients (14 percent), and therefore their dose of T4 was raised.
The conclusions of the study. GH therapy in patients with pituitary disease causes central hypothyroidism, probably by inhibiting the secretion of TSH.
The original article. Agha A, Walker D, Perry L, Drake WM, Chew SL, Jenkins PJ, Grossman AB, Monson JP. Unmasking of central hypothyroidism following growth hormone replacement in adult hypopituitary patients. Clin Endocrinol (Oxf) 2007;66:72-7.
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