Bone Abstracts

Objectives: Vertebral fractures are common in boys with DMD taking daily corticosteroids. Treatment is usually initiated when vertebral fractures have been identified. However, prophylactic treatment may be possible if reliable risk factors for vertebral fracture can be identified. The aim of this work was to compare the diagnostic accuracy of three different bone strength assessment techniques in a cohort of DMD boys.

Methods: Thirty-three boys with DMD (mean age=8.3 (S.D. 2.3) years) were followed over 3.4 (S.D. 1.8) years. All boys had size adjusted lumbar spine DXA (BMAD), distal radius peripheral QCT (pQCT) and axial QCT at baseline and DXA and pQCT at follow-up. Lateral spine imaging was performed to identify incident vertebral fractures. Mobility status and cumulative corticosteroid (CS) exposure were also recorded. Logistic regression analysis was used to identify significant predictors of vertebral fracture and diagnostic testing using a threshold of Z≤−1.0 and or age >8 years was performed with all baseline values.

Results: At baseline 31/33 boys were mobile. During follow-up 20 boys sustained 48 mild and 7 moderate vertebral fractures and 13 boys remained fracture free (FF). There were no differences in cumulative CS exposure, height, weight or body mass index SDSs but boys who remained fracture free at follow up were on average 2.1(0.7) years younger than those who suffered a vertebral fracture (VF), P=0.02. There were no significant differences in baseline or follow up LS BMAD or distal radius pQCT bone densities. In contrast, VF boys had a 1.1(0.4) S.D. lower QCT Z-score than FF boys at baseline, P=0.005. Logistic regression demonstrated that QCT Z-score was the only significant bone predictor of fracture (Exp(B) =0.4, P=0.01). However, age alone, regardless of bone density, was the strongest overall predictor of future fracture (Exp(B) =1.9, P=0.02).

Conclusion: Axial QCT is the best predictor of vertebral fracture in boys with DMD taking daily corticosteroids. Given, the progressive nature of the disease and prolonged exposure to corticosteroids, it is not surprising that age was the strongest overall predictor of fracture. However, using QCT in combination with age may be a more robust approach when considering prophylactic treatment of vertebral fractures in this population.

Disclosure: The authors declared no competing interests.