Effect of growth hormone replacement on development of hypothyroidism and hyperlipidemia

To determine the frequency with which hypothyroidism develops during human growth hormone therapy and to corroborate its onset with blood lipid changes, we measured growth rate, serum T₄ and T₃, and plasma cholesterol, triglyceride, and lipoprotein concentrations at 4-month intervals for a year in two subgroups of hGH-deficient children. The first group was initially euthyroxinemic (n=16), and the second was TSH deficient and therefore alrefore already receiving thyroxine (n=15). Basal plasma concentrations of total and low-density lipoprotein cholesterol and, to a lesser extent, plasma triglycerides were increased in both groups compared with an age-matched reference group. Basal plasma cholesterol levels were not statistically different in the euthyroxinemic and thyroxine-treated subgroups, and hGH treatment for a year did not lower lipid values in either subgroup. With hGH replacement, 25% of the euthyroxinemic patients experienced a slowdown in growth rate (3.2±0.7 cm/yr) associated with decreasing T₄ (4.8±1.1 μg/dl) and increased cholesterol concentrations (218±23 mg/dl); with thyroxine treatment, the growth rate improved (6.9±2.2 cm/yr), T₄ increased (10.0±4.0 μg/dl), and cholesterol decreased (173±44 mg/dl, P<0.05). Although our results do not justify routine thyroid replacement, they do indicate that hypothyroxinemia and hypercholesterolemia may precede the growth slowdown during hGH treatment, and the need to monitor thyroid function at this time.