Bone Abstracts

Background: In patients with osteogenesis imperfecta (OI), a rise in age-specific total body and regional bone mass is well recognised. In contrast changes in body size-adjusted bone mass in relation to changes in body composition following pamidronate therapy remain relatively unexplored.

Methods: Changes in total and regional bone mass in relation to body composition in children with OI receiving pamidronate (3 mg/kg per day over 3 days, 3 monthly) were analysed over 2 years. Subtotal body (TBLH) and lumbar spine bone mineral content (LSBMC-grams), bone area (LSBA–cm²), areal bone mineral density (LSaBMD–g/cm²), total body fat mass (grams) and lean mass (grams) were estimated by DXA in 26 children over 12 months and 17 children over 24 months. Weight, height and BMI S.D. scores were calculated using 1990 UK Child Growth Foundation data. Vertebral BMAD and volumetric BMD (BMDvol) were calculated by Carter and Kröger algorithms respectively.

Results: Age of first treatment ranged from 0.57–5.6 years (mean±S.D.=3.45±1.50). 81% (21/26) had type I OI; the remaining patients had type IV OI. There was no significant change in weight, height or BMI S.D. scores over 24 months. We observed an increase in age- and height-adjusted TBLH BMC (95%CI: 46.9, 232.5, P=0.005), LSBA (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 height and age-adjusted bone measures. 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 first year of therapy. The increase in lean mass compared to fat mass was more significant in the first year of therapy and was associated with an increase in total body bone mass. Lean mass continued to increase in the second year. We speculate that improved mobility may underlie these findings.

Disclosure: The authors declared no competing interests.