Pamidronate in children with osteogenesis imperfecta: Histomorphometric effects of long-term therapy

Context: Intravenous pamidronate treatment is beneficial to children and adolescents with osteogenesis imperfecta (OI), but the effects of prolonged therapy are not well characterized. Objective: The objective of this study was to assess the effect of long-term pamidronate treatment on the bone tissue of children and adolescents with OI. Design: This is an observational study on OI patients receiving iv pamidronate for more than 4 yr. Setting: The study was carried out in a pediatric metabolic bone research unit. Patients: Patients were 25 moderately to severely affected OI patients (seven girls) aged 1.4-15.3 yr at baseline. Intervention: Intervention was cyclical iv pamidronate at a dose of 9 mg/kg(circle)yr. Main Outcome Measures: Iliac bone biopsy and lumbar spine bone mineral density measures were obtained at treatment start, after 2.7 +/- 0.5 yr (mean +/- SD), and after 5.5 +/- 0.7 yr of therapy. Results: Average areal bone mineral density increased by 72% in the first half of the observation period, but by only 24% in the second half. Mean cortical width and cancellous bone volume increased by 87 and 38%, respectively, between baseline and the first time point during treatment (P < 0.001 for all changes). Thereafter, cortical width did not change significantly, but there was a trend (P = 0.06) toward higher cancellous bone volume. Average bone formation rate on trabecular surfaces decreased by 70% after pamidronate treatment was initiated and showed a trend (P = 0.08) toward a further decline in the second part of the study interval. Conclusion: The gains that can be achieved with pamidronate treatment appear to be largely realized in the first 2-4 yr.