Bone mineral density in children with myelomeningocele.

BACKGROUND: Difficulties with ambulation in patients with myelomeningocele often lead to physical inactivity, osteoporosis, and subsequent development of pathologic fractures. OBJECTIVE: The purpose of this study was to examine bone mineral density and biochemical markers of bone metabolism in patients with myelomeningocele. DESIGN AND METHODS: A total of 35 patients between 6 and 19 years of age with myelomeningocele (ambulatory and nonambulatory) were randomly chosen at the Texas Scottish Rite Hospital for Children. We measured bone mineral density of the distal radius in these patients using single photon absorptiometry and measured the biochemical markers of bone metabolism including parathyroid hormone, 1,25 vitamin D, osteocalcin, urinary pyridinolines/deoxypyridinolines, and urinary calcium excretion. RESULTS: Bone mineral density of the distal radius in the patients with myelomeningocele was approximately 1 to 2 standard deviation units below the mean of the normal population. There were no significant differences between ambulators and nonambulators. However, bone mineral density of the 8 patients who suffered multiple fractures (19) was significantly lower than that for those remaining patients without fractures. Elevated urinary pyridinoline levels, which indicate elevated bone reabsorption, were found more frequently in both non- and limited ambulators than in full-time ambulators. Urinary calcium excretion also was greater than twofold higher in nonambulatory patients versus ambulatory patients. There were no other differences in the biochemical markers of bone metabolism (osteocalcin, parathyroid hormone, 1,25 vitamin D, and urinary deoxypyridinolines) between ambulators and nonambulators. Bone mineral density rises in normal growing children 6 to 19 years of age. When the boys and girls were considered separately, bone mineral density rises with age in boys, but not in girls. CONCLUSION: Patients with myelomeningocele have decreased bone mineral density and are at risk of suffering pathologic bone fractures. The measurement of bone mineral density may help to identify those patients at greatest risk of suffering multiple fractures. The urinary calcium excretion of nonambulators was higher than that of ambulators and likely contributes to their decreased bone mineral density. Bone mineral density increases with age in boys, but not in girls.