Purpose or Case Report: Children with Duchene muscular dystrophy (DMD) have increased risk for osteoporosis and fragility fractures due to progressive muscle weakness with eventual loss of ambulation and chronic corticosteroid therapy. Their fracture prevalence is 40-60%, and increases with age. Bone Mineral Density (BMD) is not reflective of fracture risk. Recent studies showed that cortical thickness and area were associated with increased facture risk. Digital X-ray measurement of the cortical thickness of the metacarpal bones can be used as a marker for metacarpal cortical health. To our knowledge, this marker of bone health has not been evaluated in DMD patients. The purpose of this study was to assess bone age (BA), cortical thickness and area of metacarpal bones in relation to age in children with DMD.
Methods & Materials: In this retrospective IRB approved study, 47 boys (age range: 3-17 years; mean:11.9 ± 4.5 years) with DMD who had a bone age radiograph was included. Automated determination of bone age, and cortical bone density expressed as Bone Health Index (BHI) were performed using BoneXpert (Visiana, Holte, Denmark). Validation of bone age from Bonexpert has been performed extensively before. Z-scores were computed for bone age and BHI, and age-related changes were noted. Pearson’s correlation coefficient (r) was calculated for each metric in comparison to age.
Results: The mean z scores of bone age and BHI reduced significantly with age. Z-scores for BA and BHI were: 1) 5-8 years (n=7), BA:-0.51; BHI: -1.17; 2) 8-11 years (n=14), BA: -1.17; BHI: -1.78; 3) 11-15 years ( n=21), BA: -2.36; BHI: -1.745; 4) 15-17 years (n=4), BA:-3.77, BHI:-2.46. The Pearson’s r = -0.47 for BA and r = -0.36 for BHI (reduces with age, p<0.005). The actual BHI with age was: 1) 5-8 years BHI: 3.86 ± 0.38; 2) 8-11 years; BHI: 3.83 ± 0.35; 3) 11-15 years BHI: 3.76 ± 0.95; 4) 15-17 years ; BHI: 3.84 ± 0.32
Conclusions: We showcase a new metric that looks at bone health in DMD children, and demonstrate a worsening BHI with age in DMD patients. BHI may have values in assessment of bone health in children with DMD. The worsening BHI with increasing age may correlate with increased fracture risk that is known to increase over time due to disease progression and longer corticosteroid exposure. Future study is needed to determine the association of BHI and fracture risk.