Bone health and vitamin D metabolism in children and adolescents with Duchenne muscular dystrophy compared with other neuromuscular diseases and cerebral palsy

Aims: Underlying disease, inactivity, and vitamin D deficiency are possible causes for low bone density, a condition which has been found in children with muscular dystrophy and cerebral palsy. Subsequent fractures in Duchenne patients can lead to premature loss of ambulation.

Methods: We classified the ambulatory status of three patient groups (20 Duchenne muscular dystrophy [DMD] patients; 13 patients with other neuromuscular disorders [NME]; 20 with cerebral palsy [ICP]) using the GMFCS, CIDD-Score and a compounded, disease-spanning scale, plus time-based measurements of Gower maneuver and 10-m walking distance. The areal bone mineral density (aBMD) was measured using dual-energy X-ray absorptiometry (General Electric, Lunar Prodigy) at the lumbar spine, providing age-, sex- and height-adjusted Z-scores based on a normative database. Vitamin D and calcium substitutions, daily intake and levels in blood, as well as relevant markers of bone turnover in serum and urine were recorded.

Results: Almost all patients displayed low bone mineral density values. In the DMD group, a linear decrease of aBMD after loss of ambulation was measured correlating with the degree of ambulatory ability. The aBMD and ambulatory status of the DMD group differed significantly from the ICP group. No significant group differences could be demonstrated regarding age, height and height percentiles, tanner stage, Z-score, vitamin D- and calcium-serum levels. Linear regression analysis identified tanner stage and ambulatory status as independent variables affecting aBMD, and height percentiles influencing the Z-score.

Conclusion: Low bone mineral density in disabled children is determined by their level of physical maturity and level of disablement regardless of the disablement###s etiology. The vitamin D levels of our patients were low but comparable to those of healthy children in Germany without any correlation to BMD. There were no signs of reduced bone health due to rickets. Therapeutically, we thus recommend promoting the ambulatory status as long as possible and considering prophylactic vitamin D and calcium substitutions.