OSTEOPOROSIS
Osteoporosis is the pathologic reduction of bone matrix and minerals, whereas osteopenia is a reduced density of bone. Osteoporosis has been identified as a medical problem in the adult with myelomeningocele (136).
Although typically considered an adult disease, osteoporosis is a disease that starts in childhood (137,138). The age at which abnormalities in bone mineral density (BMD) first present in the spina bifida population is not known. It has been reported that children with myelomeningocele have a higher fracture risk and that those individuals who fracture have a lower bone density than age-matched peers (139). In patients with myelomeningocele, fractures typically occur in the long bones of the lower extremity, most commonly in the femur and less so in the tibia (140,141). Recent data suggest that fractures are present at all levels of spina bifida, with an annual incidence of about 3%. The age for first fracture was around 11 years, with the tibia and femur most involved. Of those with fractures, 1 out of 4 reported multiple fractures (119).Most contemporary studies of osteoporosis utilize dual energy x-ray absorptiometry to assess bone density. Non-weight bearing conditions such as cerebral palsy (CP), Duchenne muscular dystrophy (DMD), and spinal cord injury have been shown to be associated with decreased BMD that can result in fractures, even in the pediatric population (142-144). It has been shown that BMD of the lumbar spine and proximal femur in children often correlates poorly, particularly if BMD is low (145). Studies currently have found utility in assessing the BMD in the lateral distal femur, as the lower extremities are a common site of fracturing (146). Recently published studies in patients with myelomeningocele attempt to describe the effect of non-weight bearing on BMD; however, these studies have been limited by small sample size, inclusion of a limited number of pediatric patients with myelomeningocele, and older technology (138,139,147-149).
There may be technical difficulties in obtaining adequate lumbar spine and proximal femur assessments due to vertebral abnormalities and hip deformities (150).
Treatment
Toddlers (age 1-3 years) require about 500 mg of calcium each day. Preschool and younger school-age children (age 4-8 years) require about 800 mg of calcium each day. Older school-age children and teens (age 9-18 years) require about 1300 mg of calcium each day. This guideline is set by American Academy of Pediatrics (AAP) to meet the needs of 95% of healthy children (151,152).
There are limited natural dietary sources of vitamin D, and adequate sunshine exposure for the cutaneous synthesis of vitamin D is not easily determined for a given individual. In addition, sunshine exposure increases the risk of skin cancer, and decreased sun exposure is not uncommon for individuals with disabilities. The recommendations from the AAP have been revised to ensure adequate vitamin D status. It is now recommended that all infants and children, including adolescents, have a minimum daily intake of 400 IU of vitamin D beginning soon after birth. The current recommendation replaces the previous recommendation of a minimum daily intake of 200 IU∕day of vitamin D supplementation beginning in the first two months after birth and continuing through adolescence. These revised guidelines for vitamin D intake for healthy infants, children, and adolescents are based on evidence from new clinical trials and the historical precedence of safely giving 400 IU of vitamin D per day in the pediatric and adolescent population (153).
In the setting of osteopenia or osteoporosis, individuals' vitamin D status and dietary history should be evaluated. Any deficiencies should be treated. Weightbearing activities should be encouraged; however, there has been little to no data in regard to stander use in the spina bifida population. Standing weightbearing exercises or activities can apparently increase BMD in the lumbar spine or femur in children with cerebral palsy (154,155).
Treatment for pathologic fractures supports the use of medication such as bisphosphonates. Prevention is key, and careful attention to daily calcium and vitamin D intake, as well as a standing or walking program for those that are nonambulatory, is essential to minimize the reduction in bone density and the fracture risk (156).
More aggressive pharmacologic therapies have been used in other pediatric patient groups for the treatment of osteoporosis. The current treatment garnering most interest is the bisphosphonates. Bisphosphonate use has not been studied in the spina bifida population, but there has been increased use in pediatrics (157,158).