Osteopenia/Pathologic Fractures

Children with special health care needs may have osteopenia for several reasons. These include decreased mobility, decreased calcium and/or vitamin D intake, delayed puberty, and medications, especially some of the antiepileptic medications [Pack: 2003] [Valsamis: 2006] [Sheth: 2004] [Farhat: 2002] that cause osteoporosis. Children with these risk factors may be at increased risk for pathological fractures that may occur with low forces to their bones, such as positioning for Xrays and physical therapy. Children with CP have a higher fracture rate than the general population [Stevenson: 2006] and this fracture rate may be even higher in children with CP on antiepileptic medications [Leet: 2006]. Fractures are increased two to six times in patients with epilepsy compared to the general population. [Mattson: 2004] [Vestergaard: 1999] As many children who start on antiepileptic medications in childhood will be on those medications for many years, the fracture risk by adulthood is substantial. The enzyme inducing drugs phenobarbital, carbamazepine, phenytoin and benzodiazepines such as klonopin and valium decrease bone density through effects on vitamin D metabolism and subsequent hypocalcemia. [Valsamis: 2006] Valproic acid is thought to directly act on the bone, increasing activity of the osteoclasts, the cells responsible for bone breakdown in the dynamic process of remodeling. [Valsamis: 2006] Not as much information is available regarding the newer antiepileptic drugs, but preliminary reports are favorable. [Farhat: 2002]

Surveillance
Children who are at risk should be assessed by DEXA scan (Dual-energy X-ray Absorptiometry), which is a non-invasive test that measures bone density and compares it (by Z-score) with bone density in children of the same age and gender, approximately yearly. Although there are problems interpreting these numbers in children, the fracture risk does correlate with the bone mineral density. The DEXA scan involves radiation, but it is not painful, does not require sedation, and is relatively fast. DEXA scans should be ordered as a baseline when the child is non-mobile or has other risk factors, and then yearly or bi-yearly depending on results and risk factors. Children who have already had fractures should be followed more closely. Serum calcium, phosphate, alkaline phosphatase, PTH and vitamin D levels should also be measured periodically. [Valsamis: 2006]

Treatment
Children with these risk factors should have diet optimized for vitamin D and calcium. See Calcium and vitamin D (general). Children who are non-mobile should be mobilized as much as possible with walkers, etc. Children who are confined to wheelchairs should spend an hour, or more if possible, in a stander. Exercise should be encouraged, and swimming might be especially good in children who are confined to wheelchairs. If fractures have already occurred without sufficient force that the fracture would probably have occurred in a child with typical development, and possibly even if Z-scores for bone density are low and there have not been any fractures, treatment may be beneficial. This involves treatment with bisphosphonates, although other medications not currently approved in children may be available in the future.

Bisphosphonate treatment may either be parenteral (IV pamidronate, q 2-4 months) or oral (most of the experience with children is with alendronate, 35 mg for children under 40 kg, 70 mg for those over 40 kg, q week). Before starting therapy with bisphosphonates, laboratory tests for ionized calcium, phosphate, alkaline phosphatase, iPTH, 1,25(OH)2D3 in serum and calcium, creatinine, and phosphate in urine should be performed to rule out abnormalities that might prevent therapy with these agents. As alendronate is taken weekly on an empty stomach while the child is sitting (either supported in a wheelchair or independently) for 30 minutes before eating with a full glass of water, children who will take alendronate need to be able to fulfill these criteria. Alendronate can cause esophagitis and is not absorbed well when food is present, so these directions need to be followed closely. Bisphosphonates have been associated with a rare side effect, osteonecrosis of the jaw. Children who are going to be taking bisphosphonates should be seen regularly by a pediatric dentist with caries and other oral problems treated as this might minimize the possibility of osteonecrosis of the jaw. Consideration of an endocrinology consultation should be given when children on antiepileptic medication have fractures and/or low bone mineral densities.