Bone Health Determinants in Ambulant Prepubertal Boys With Duchenne Muscular Dystrophy Treated With Deflazacort: Findings From a 3-Year Study

Introduction/aims: Duchenne muscular dystrophy (DMD) is complicated by bone fragility. This study aimed to elucidate changes in bone mineral density (BMD) and body composition over time and to explore associations with adiposity measures in DMD.

Methods: A three-year follow-up analysis was performed of total body (TB) and lumbar spine (LS) dual-energy x-ray absorptiometry (DXA) measurements, anthropometric measures, Tanner stage and bone turnover biomarkers assessments, and the incidence of fragility fractures in 26 ambulant prepubertal DMD patients treated with deflazacort (DFZ).

Results: Age at baseline was 7.7 years (interquartile range: 6-9.2). The TB BMD Z-score declined over time and was negatively related to the TB fat mass percentage and fat mass index (p < 0.05), but not to body mass index (BMI) standard deviation score (SDS). In contrast LS bone mineral apparent density (BMAD) Z-score remained stable and normal. The cumulative incidence of fragility fractures was 19.2%; DMD boys with fractures displayed a 1.5-fold higher decline of TB BMD Z-score/year (p < 0.05) and a worse adiposity profile compared to fracture-free patients. No difference was found in DFZ dose or duration between the two groups.

Discussion: We observed a high incidence of fragility fractures, and identified fat tissue as a potential detrimental factor for bone health, suggesting a need for monitoring in DMD patients with excessive adiposity. Fat mass measures assessed by DXA could help to identify those at risk, enabling targeted interventions for better bone health. The co-occurrence of multiple glucocorticoid side effects might characterize patients at higher risk of fractures.