P.2.18 Bone mineral density and bone mineral content as measures of bone health in ambulatory boys with Duchenne Muscular Dystrophy

Abstract

Osteoporosis is a major problem in Duchenne Muscular Dystrophy (DMD) due to long term glucocorticoid (GC) therapy and impaired mobility. Dual-energy xray absorptiometry (DXA) assessment of bone health in DMD boys is challenging, as interpretation is affected by height, delayed bone maturation, puberty, and vertebral fractures. Accurate detection and intervention of osteoporosis are important for improving clinical care in DMD. To assess changes in bone mineral density (BMD) and bone mineral content (BMC) by functional status in ambulatory GC-treated DMD boys. Retrospective study of whole body (WB) and lumbar spine (LS) BMD and BMC by DXA in ambulatory GC-treated DMD boys, assessed from 2/2009 to 7/2012. Bisphosphonate-treated boys were excluded. Age-adjusted z-scores (Z) and height-adjusted z-scores (HAZ) were derived using normal values. Generalized linear modeling was used to analyze changes in BMD and BMC by functional status (functional mobility score, FMS1, 2 or 3, by worsening status). 277 ambulant DMD boys were grouped by FMS (mean ages ±SD for FMS1, 2 and 3; 7.6±2.2, 8.3±2.6 and 11.2±2.6yrs). GC durations for FMS1, 2 and 3 were 2.7±1.7, 2.9±2.1 and 5.3±2.6yrs. For whole body, BMD-Z, BMD-HAZ, BMC-Z and BMC-HAZ all decreased with worsening FMS (p<0.05 for FMS3 vs. FMS1 or FMS2). WB BMC was consistently lower than WB BMD for each FMS group. For spine, BMD-Z was similar between FMS groups, but BMC-Z was lower for FMS3 than FMS1 or FMS2 (<i>p</i><0.05). LS BMD-HAZ was surprisingly higher for FMS3 than the other groups, but LS BMC-HAZ remained similar between groups. WB bone indices worsened with declining mobility and increased GC duration. BMC was consistently lower than BMD, and spine BMC showed a relative decrease compared to BMD in weaker boys. Our study suggests that BMC may be a more sensitive indicator of bone health in DMD, and should be considered in conjunction with BMD as part of clinical care.