Bone Abstracts

Childhood and adolescence are critical periods for optimizing bone growth and mineral accrual. Bone strength is determined by bone size, geometry, quality, and mass – variables that are influenced by genetic factors, physical activity, nutrition, and pubertal hormones. Duchenne muscular dystrophy (DMD) and cerebral palsy (CP) are two chronic medical conditions of childhood associated with reduced mobility and increased rate of pathological fracture.

DMD is an X-linked disorder of muscle limited to males. Chronic and progressive immobilization is an inevitable consequence of DMD. Corticosteroids assist in keeping boys with DMD more mobile but also result in inevitable and progressive bone loss and increased fracture risk, both in the axial and appendicular skeleton.¹ Long-bone and vertebral fracture are seen in up to 75 and 30% of boys respectively.¹ Of major concern, as many as 20–50% of boys ambulant prior to the fracture, lose their ability to walk after the fracture¹.

CP is the most common cause of physical disability in childhood with a prevalence of approximately one in 500 children. Mobility and areal bone mineral density (aBMD) decline and fracture risk increases with increasing age in children with CP.^1,5 Costs of care, the burden placed upon families and risk of osteoporotic fracture all increase as immobility increases in CP.^5,6

Bisphosphonates are being administered with increasing frequency to children with secondary osteoporosis.⁵ There are a paucity of controlled trials of bisphosphonates in children with DMD or CP. Available data would suggest bisphosphonates increase BMD, but there is little to suggest that they reduce fracture rate. RCTs are currently underway to address this. Novel treatment approaches in DMD and CP include the use of whole body vibration plates, RANKL inhibitors and anti-sclerostin antibodies. Early intervention to maintain mobility is critical in ambulant children with CP.

This presentation will address the mechanism underlying bone fragility in DMD and CP, data on fracture risk and current and future treatment options.

Disclosure: Receipt of grants/research support: Amgen, Novartis.

References

1. McAdam LC, Mayo AL, Alman BA & Biggar WD. The Canadian experience with long-term deflazacort treatment in Duchenne muscular dystrophy. Acta Myol 2012 31 (1) 16–20.

2. Henderson R et al. Growth and nutritional status in residential centre versus home-living children and adolescents with quadriplegic cerebral palsy. J Ped 2007 151 (2) p161–p166.

3. Fowler E et al. Promotion of physical fitness and prevention of secondary conditions for children with cerebral palsy: APTA Pediatric Research Summit. Phys Ther 2007 87 (11) 1495–1510.

4. Chen C et al. Factors associated with bone density in different skeletal regions in children with cerebral palsy of various motor severities. Develop Med Child Neurol 2011 53 131–136.

5. Simm PJ et al. Zoledronic acid improves bone mineral density, reduces bone turnover and improves skeletal architecture over 2 years of treatment in children with secondary osteoporosis. Bone 2011 49 (5) 939–943.