Osteogenesis imperfecta: Anthropometric, skeletal and mineral metabolic effects of long-term intravenous pamidronate therapy

Background: Administration of bisphosphonates represents a beneficial therapy in children and adolescents with severe osteogenesis imperfecta (OI) because it significantly reduces the annual rate of bone fractures. Aim: To evaluate the anthropometric, skeletal and mineral metabolic effects of long-term intravenous pamidronate therapy in OI. Methods: Ten patients, aged 5 mo to 25 y, with OI received cyclical intravenous pamidronate. The yearly dose of pamidronate was approximately 9 mg/kg/d at all ages. Duration of treatment varied from a minimum of 2 y to a maximum of 5 y. Growth, bone mass and mineral metabolic parameters were studied at baseline and repeated every year thereafter. Bone mass was assessed by calculation of bone mineral apparent density (L-2-/L-4 BMAD). This represents the first study on the changes in size-adjusted measures of bone mass observed with such therapy. Results: While on therapy, all children and adolescents grew normally but did not experience any manifest catch-up growth. A significant decrease in the incidence of bone fractures was observed. In seven patients with severe forms, L-2-/L-4 BMAD increased by 80% after the first 2 y of therapy but tended to stabilize or even decrease over the following years despite maintenance of therapy. A significant inverse correlation could be established between urinary Ca excretion and L-2-/L-4 BMAD (r = -0.30, p < 0.05). Conclusion: Our results confirm that cyclical pamidronate infusions reduce the incidence of bone fractures and allow normal growth. The improvement in bone mass initially observed after the first 2 y of therapy is not always sustained over the following years despite maintenance of therapy.