Background: GH-deficient patients respond to recombinant human GH (rhGH) replacement therapy by increasing bone mineral density (BMD) at a rate of about 1% a year for at least 4 years. Predictive factors for a beneficial effect on bone are a low bone mass at baseline and gender. Whether the beneficial skeletal effects of GH are sustained in the long term remains to be established. It is also not known whether osteoporotic GH-deficient patients may require additional antiresorptive drugs and whether this treatment would be effective concomitantly with GH replacement.
Design: We performed a long-term, controlled study in 30 GH-deficient adults: 15 with osteoporosis and 15 control subjects with low bone mass. All patients were treated with rhGH for at least 4 years; thereafter, 3 years of additional alendronate treatment was given to patients with osteoporosis, while controls continued on GH therapy alone. The GH dose was individualized to maintain an IGF-I within the normal reference range for the duration of the study, and was equal between genders.
Results: At the end of 4 years of rhGH replacement therapy, a significant increase in mean lumbar spine BMD was observed in both the osteoporosis group (3.6%) and the control group (7.0%), with no significant difference between groups. Males had a larger increase in BMD than females (P = 0.032). After 4 or 5 years of GH treatment patients with persisting osteoporosis received additional alendronate (10 mg/day) for 3 years. Lumbar spine BMD increased by 8.7% after 3 years (P = 0.001) vs 1.5% (P = NS) in the control group continuing on rhGH replacement alone. The alendronate effect was gender independent (P = 0.59). Mean bone area of the lumbar spine did not change in both groups for the duration of the study. Femoral neck BMD increased significantly in the osteoporosis group (3.5%) and was unchanged in the control group. Five osteoporotic GH-deficient patients had a total of 12 vertebral fractures before start of alendronate. Only one of these patients developed two new vertebral fractures within the first year of treatment with alendronate.
Conclusion: We observed a significant increase in lumbar spine BMD in the first 4 years of rhGH replacement. The effect of GH on bone was gender dependent, but not BMD dependent. After more than 4 years of GH replacement, BMD seemed to reach a plateau, at least as measured in the 3-4 years thereafter, as no significant increase was present in patients treated with GH alone. By contrast, alendronate rapidly augmented BMD and this effect was maintained for at least 3 years. These increases in BMD were associated with a low incidence of (vertebral) fractures. The long-term use of GH does not preclude a beneficial effect of an additional antiresorptive agent in GH-deficient patients with osteoporosis.