Bone mineral density and vitamin D status in ambulatory and non-ambulatory children with cerebral palsy.

Abstract

This study assessed distal femur and lumbar spine bone mineral density (BMD) Z-scores in children with cerebral palsy. BMD z-score was lower in non-ambulatory than in ambulatory children. Somewhat surprisingly, among ambulatory children, those with better walking abilities had higher BMD z-score than those with more impaired walking ability. Children with cerebral palsy (CP) have increased risk for low bone mineral density (BMD). The aim was to explore the difference in BMD at the distal femur and lumbar spine between ambulatory and non-ambulatory children with CP and the relationship between vitamin D status and BMD. Fifty-one children (age range 8-18years; 20 girls) with CP participated. Their BMD Z-scores were measured in the lumbar spine and the distal femur using dual X-ray absorptiometry, and 25-hydroxy-vitamin D (25-OHD) concentrations were measured in serum. Children with GMFCS level I-III were defined as 'walkers' while children with level IV-V were defined as 'non-walkers. Non-walkers had lower mean BMD Z-scores (range -1.7 to -5.4) than walkers at all sites (range -0.8 to -1.5). Among walkers, BMD Z-scores at the distal femur were lower in those with GMFCS level II than with level I (p values < 0.004). A similar difference was found between the affected and unaffected limb in children with hemiplegia. Mean 25-OHD concentration was 45nmol/L (SD = 18); lower in walkers (mean = 41nmol/L; SD = 18) than in non-walkers (mean = 53nmol/L; SD = 19; p = 0.041). There were no correlations between 25-OHD and BMD z-scores. The main predictor of low BMD Z-scores in the distal femur was the inability to walk, but the results suggest that the degree of the neuromotor impairment may also be a significant predictor. Vitamin D status did not correlate with BMD z-scores.