Bone Density Evaluation in Teens Prevents Future Osteoporosis

[Admin]

October 13, 2006 — A review published in the October issue of the Archives of Pediatrics & Adolescent Medicine describes the most effective methods to evaluate bone density in teens to prevent future osteoporosis.

"Pediatric and adolescent care professionals have increasingly recognized the importance of understanding the skeletal health of their patients," write Keith J. Loud, MDCM, MSc, from the Children's Hospital Medical Center of Akron in Akron, Ohio, and Catherine M. Gordon, MD, MSc, from Children's Hospital Boston in Boston, Massachusetts. "Peak bone mass, the 'bone bank' on which an individual will draw for their entire adult life, is likely achieved by late adolescence, with the critical window for accumulation occurring much earlier."

This review covers known conditions associated with impaired bone mineral accrual; clinical settings in which the evaluation of "at-risk" adolescents should be considered; available methods for evaluating bone density and their respective limitations; and potential therapeutic options for patients diagnosed with low bone mineral density (BMD). The authors also review current recommendations regarding physical activity and nutrition, which should benefit all adolescents.

Bone health in adolescents may benefit from exercise, which is "site specific," in that the response of the skeleton varies depending on the type of exercise studied. Nutritional factors also affect bone density and bone accretion during adolescence. Overweight children have an increased incidence of fractures, whereas illnesses characterized by weight loss, such as anorexia nervosa, illustrate the detrimental effect of malnutrition on bone density in teenagers.

The effect of calcium intake during adolescence is one of the most intensely studied areas of pediatric bone health, and experts now recommend providing optimal calcium intake to maximize peak bone mass. Calcium absorption is enhanced during puberty, with an optimal calcium balance achieved at an intake of approximately 1300 mg/day. However, most adolescents fail to achieve the recommended daily intake. Vitamin D deficiency is a common problem among otherwise healthy young patients, but this deficiency is not correlated definitively with decreased bone density in youth, often because of the lack of BMD measurements in some studies.

Endogenous circulating estrogens and androgens have independently positive effects on bone growth, development, and mineral acquisition for both male and female adolescents. Growth hormone deficiency reduces bone size and mass, and other endocrinopathies affect the bone remodeling cycle. Avoiding excessive alcohol and any tobacco use benefits bone health.

Conditions increasing the risk for poor skeletal health in adolescents (other than intrinsic bone diseases such as osteogenesis imperfecta) include cystic fibrosis, inflammatory bowel disease, use of medications with harmful skeletal effects, "athletic amenorrhea," and any condition that negatively affects the factors described above.

BMD has been the most commonly used outcome measure to address skeletal status and fracture risk. Dual-energy x-ray absorptiometry (DEXA) is the current standard for assessing BMD in children and adolescents. However, a pediatric normative database must be used to interpret properly the measurement for either bone mineral content or BMD. The diagnosis of osteoporosis in children requires evidence of skeletal fragility and should not be made based on DEXA measurements alone.

The current "gold standard" for noninvasive bone evaluation is quantitative computed tomography (QCT), which can evaluate bone in 3 dimensions. However, normative pediatric data are sparse, with their use reserved primarily for research. Quantitative ultrasound involves no radiation exposure, is portable, and potentially allows for inexpensive, office-based bone health screening, but not all quantitative ultrasound devices are appropriately sized for use in children and younger adolescents, and most lack adequate normative pediatric databases.

QCT can best measure bone strength, which depends on bone mass, size, geometry, and microarchitecture. Magnetic resonance imaging may be a radiation-free alternative to evaluate both bone geometry and quality, and there are mathematical models using DEXA data to estimate bone strength at the hip.

Although serum and urinary markers of bone turnover are sensitive to changes in bone formation and resorption, variability in these measures during adolescence mandates that their use be restricted to monitoring treatment effects rather than diagnosis. Common measures of calcium homeostasis do not directly reflect bone turnover, but they may be useful when evaluating low BMD, in conjunction with body mass index calculation and Tanner staging. Bone biopsy may rarely be indicated for particularly challenging cases.

No evidence-based clinical guidelines currently exist to help healthcare professionals determine when BMD screening is warranted, although several groups have published recommendations. DEXA scanning should be considered for an adolescent with an underlying chronic condition that predisposes to a low BMD. The presence of multiple risk factors or a strong family history of osteoporosis should lower the threshold for evaluation.

"There are few skeletal agents (medications designed to augment BMD by either inhibiting bone resorption and/or increasing bone formation) available for potential use in adolescents," the authors write. "The unknown effects of some of these medications on a growing skeleton and the disappointing efficacy of others has hindered their use by pediatric professionals.... Because it is known that bisphosphonates remain in the skeleton for several years, perhaps indefinitely, and that they cross the placenta, health care professionals should proceed with caution until more definitive safety and efficacy data are available."

Potentially beneficial interventions for all adolescents include physical activity (high-intensity impact activities, such as running, jumping, gymnastics, or basketball for 10 to 20 minutes, at least 3 days per week), and 200 IU or more of vitamin D supplementation daily.

"Adolescence is the most critical period across the life span for bone health because more than half of PBM [peak bone mass] is accumulated during the teenage years," the authors conclude. "Recent and ongoing studies have highlighted the increasing number of clinical settings in which an adolescent may potentially lose bone density and are beginning to fill gaps in knowledge regarding the roles of physical activity and calcium and vitamin D intake in healthy adolescents, as well as the appropriate use of pharmacologic skeletal agents in those with chronic illness. Unfortunately, research has not yet generated evidence to identify appropriate candidates for both baseline bone density screening and continued monitoring."

The National Institutes of Health and Department of Health and Human Services supported this work in part.

Arch Pediatr Adolesc Med. 2006;160:1026-1032.

Source: http://www.medscape.com/viewarticle/545997?src=0_nl_cme_9