Endocrine Abstracts

Background: The role of bisphosphonates in improving bone mass in patients with osteogenesis impefercta (OI) is well established. However, the impact of bisphosphonate therapy on body composition in relation to increasing bone mass remains relatively unexplored.

Methods: Change in DXA-derived subtotal body (TBLH) and lumbar spine (LS: L1–L4) bone mineral content (BMC (g)), bone area (BA (cm²)), areal bone mineral density (aBMD (g/cm²)) adjusted for age and height, and age-adjusted volumetric bone mineral apparent density (BMAD), total body fat mass (g), and lean mass (g) were calculated in 26 children with OI after 1 year and in 17 children after 2 years of bisphosphonate therapy. Patients received i.v. pamidronate (3 mg/kg per day) over 3 days every 3 months.

Results: Age of first treatment ranged from 0.57 to 5.6 years (mean±S.D.=3.45±1.50). 81% (21/26) had type 1 OI; the remaining patients had type 4 OI. There was no significant change in height or BMI SDS over 24 months. There was an increase in age- and height-adjusted TBLH BMC (95% CI: 46.9–232.5, P=0.005), BA (95% CI: 126.8–359.1, P<0.001), LSaBMD (95% CI: 0.02–0.216, P=0.02), and age-corrected BMAD (95% CI: 0.0001–0.013, P=0.05) over 12 months. From 12 to 24 months there was no change in the adjusted bone parameters. Total body fat mass (95% CI: 17.3–657.5, P=0.04) and lean mass (95% CI: 446.5–1490.8, P=0.001) significantly increased after 12 months of therapy but only lean mass continued to increase from 12 to 24 months (95% CI: 232.0–1702.3, P=0.01). In the first 12 months, change in lean mass was associated with an increase in TBLH BA (95% CI: 0.04–0.69, P=0.03) and TBLH BMC (95% CI: 0.22–0.77, P=0.004).

Conclusions: Pamidronate had the greatest impact on size- and age-adjusted total body and lumbar bone mass in the 1st year of therapy. Increase in muscle mass may augment overall increases in bone mass and size in children with OI. We speculate that improved mobility may underlie these findings.