Monday, January 3, 2011

AAP Issues Guidelines on Bone Densitometry in Children and Adolescents

From Medscape Medical News

Laurie Barclay, MD

January 3, 2011 — The American Academy of Pediatrics (AAP) has issued clinical guidelines regarding the use, interpretation, harms, and costs of bone densitometry in children and adolescents. The new recommendations are reported online December 27, 2010, in a clinical report in Pediatrics.

"Concern for bone fragility in children and adolescents has led to increased interest in bone densitometry," write Laura K. Bachrach, MD; Irene N. Sills, MD; and colleagues from the AAP Section on Endocrinology. "Pediatric patients with genetic and acquired chronic diseases, immobility, and inadequate nutrition may fail to achieve the expected gains in bone size, mass, and strength, which leaves them vulnerable to fracture. In older adults, bone densitometry has been shown to predict fracture risk and reflect response to therapy, [but] the role of densitometry in the management of children at risk of bone fragility is less certain."

Recommendations highlighted in the AAP clinical report were based on consensus statements developed by an international panel of bone experts convened at the 2007 Pediatric Position Development Conference of the International Society of Clinical Densitometry. Whenever possible, the recommendations were evidence based, but others reflect expert consensus because existing evidence was insufficient.

Indications for Bone Densitometry in Children

Specific recommendations regarding indications for use of bone densitometry in the pediatric population include the following:

* Dual-energy x-ray absorptiometry (DXA) of the lumbar spine and total body is the recommended test to determine bone density in children because of high availability, reproducibility, speed, low levels of radiation exposure, and availability of a pediatric reference database.
* Children with primary bone disorders (idiopathic juvenile osteoporosis and osteogenesis imperfecta) and secondary disorders linked to an increased risk for fracture should undergo densitometry when they are first seen and before bone-active therapy is started. Secondary conditions include chronic inflammatory diseases, immobilization for long periods, endocrine or hematologic diseases, and cancer and associated treatments that adversely affect bone.
* Children with a history of clinically significant fracture (1 lower extremity long-bone fracture, ≥ 2 upper extremity long-bone fractures, or vertebral fracture after minimal or no trauma) should undergo DXA scanning. Bone mineral density (BMD) measurement may be indicated, depending on patient age at fracture, severity of any underlying conditions, associated risk factors, exposure to ionizing radiation or drugs adversely affecting bone, exposure, family history, number of fractures, and trauma intensity, with low trauma fractures defined as those involving a fall from standing height or less.
* In children, the lumbar spine and total body (excluding the cranium, if possible) are the preferred sites for DXA testing. Children with contractures may need to be tested at the lateral distal aspect of the femur, and those with metal hardware may need to be tested at other sites for children.
* Although 6 months should normally elapse before densitometry testing is repeated, it might be appropriate in some cases to wait at least 1 year.

Interpretation of Results

Specific recommendations concerning interpretation of results for use of bone densitometry in the pediatric population are as follows:

* In children, suggested diagnostic criteria for osteoporosis are a clinically significant history of fracture and low bone mass with bone mineral content (BMC; in grams) or BMD (in grams per centimeter squared) z score of more than 2 SDs below that expected from DXA reference data for healthy persons of similar age, sex, and race or ethnicity, if possible. Such data are available for children and teenagers but not for infants. For children with chronic illness or delayed puberty, BMD should be adjusted based on height or should be compared with reference data specific for age, sex, and height.
* BMC, BMD, and estimated volumetric BMD are more likely to be lower in healthy children with a history of fractures vs those with no history of fractures.
* Data regarding the association between low bone mass and fracture risk are limited for children with chronic illness.

Risks and Costs

Specific recommendations regarding risks and costs of bone densitometry in the pediatric population include the following:

* Children undergoing spine and total body DXA may be exposed to 5 to 6 μSv of ionizing radiation, which is not known to be associated with health risk.
* If DXA data are not interpreted by skilled professionals at pediatric densitometry centers, there is a potential risk for misdiagnosis, including a high percentage of errors involving a misdiagnosis of osteoporosis on the basis of inappropriate use of a T score.
* Errors in DXA interpretation may result in avoidable parental concern and in expensive and unnecessary use of drugs and restrictions on physical activity.

"DXA has been established as a valuable tool as part of a comprehensive skeletal assessment of children and teenagers but not yet of infants," the guideline authors write. "Acquiring and interpreting densitometry data from younger patients remains challenging and should be performed in experienced pediatric densitometry centers."

"Panels of pediatric experts have set standards for when and how to perform DXA scans on the basis of the best available data," the guideline authors conclude. "Ongoing research will serve to refine the best modalities for assessing the bone strength of children and to determine the key clinical variables that influence fracture risk independent of bone."

The AAP supported development of this clinical report and evaluated any potential conflicts of interest of its authors.

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