Further increase in forearm cortical bone mineral content after discontinuation of growth hormone replacement.

Abstract

OBJECTIVE: Growth hormone replacement of adults with childhood onset GH deficiency results in an increase in bone mineral density (BMD) after 6-12 months of GH replacement. By measuring BMD 12 months after discontinuation of GH replacement we aimed to investigate whether there is an effect of GH replacement on BMD persisting after GH has been withdrawn. DESIGN: BMD was measured 13 +/- 1 (mean +/- SE, range 11-16) months after discontinuation of GH replacement. PATIENTS: Ten adults, age 23.2 +/- 1.4 (range 18.8-32.4) years, with childhood onset isolated GH deficiency (2 idiopathic, 8 irradiation induced) who had previously completed a study of the effect of 12 months of GH replacement on BMD. MEASUREMENTS: Forearm cortical bone mineral content (BMC) was measured using single-photon absorptiometry at the proximal site of the distal forearm. Forearm integral BMC at the ultradistal site of the forearm and bone width at both proximal and ultradistal sites of the distal forearm were measured by the same technique. Vertebral trabecular BMD was measured using quantitative computed tomography. RESULTS: Forearm cortical BMC was significantly greater than that measured at the time of discontinuation of GH (1.48 +/- 0.04 vs 1.44 +/- 0.05 g/cm). There was no significant change in forearm integral BMC or in vertebral trabecular BMD after discontinuation of GH. There was no significant change in bone width at proximal and ultradistal sites of the distal forearm after discontinuation of GH. CONCLUSION: After discontinuation of GH replacement the further increase in forearm cortical bone mineral content without a significant increase in forearm bone width suggests that the increase in cortical bone mineral content is due to a persisting effect of previous GH replacement, and not to further spontaneous attainment of bone mass before peak bone mass is reached. These findings emphasize the importance of continuing to monitor bone mass after the stimulus to increase bone turnover has been withdrawn.