Objectives: To compare and contrast the natural history of osteoporosis and response to zoledronate in children and adolescents with Duchene muscular dystrophy (DMD), spinal muscular atrophy (SMA) or other congenital muscular dystrophies (CMD).
Methods: A retrospective medical record review of fracture history, treatment and bone mineral densitometry of children managed at a tertiary centre in Sydney over the last 6 years.
Results: A total of 115 children/adolescents were included in this study. Diagnoses included DMD (n=50), SMA (n=25) or CMD (n=40). Mean age at first DXA was 8, 8.4 and 8.5 years, respectively. 86% of children with DMD were already on glucocorticoids at baseline DXA compared to <5% of those with SMA/CMD. All children were bisphosphonate naïve at baseline DXA. Children with SMA were significantly shorter than DMD/CMD but height-adjusted total body BMD (tBMD) was lowest in the DMD group (mean Z-score −0.5). Bone area was smallest in those with SMA (mean Z-score −3). Vertebral compression fractures were more evident in the DMD group. Serial DXAs were performed up to a mean age of 15 years. Over that timeframe, 25 (50%) with DMD were treated with zoledronate, 5 (20%) with SMA and 10 (25%) with CMD. Zoledronate did not significantly alter fracture rates but improved tBMD Z-scores by a mean of 0.51 and spine BMD Z-scores by a mean of 11.5 across the groups. In children not treated with bisphosphonates, there was a mean decline in tBMD and spine BMD Z-scores of 0.51.5, which was related to ability to stand rather than underlying neuromuscular condition.
Conclusion: Standing/weight-bearing remains a vital component in preserving tBMD but there are significant improvements in all groups with the use of bisphosphonates. Despite this, the ubiquitous use of glucocorticoids in DMD may be responsible for the increased vertebral compression fractures in this group. Further studies are required in order to determine the optimal treatment regimen in children and adolescents with neuromuscular disease and identify criteria for potential prophylactic bisphosphonate use.
Disclosure: The authors declared no competing interests.