Bone Density Evaluation in Teens Prevents Future Osteoporosis

[center]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/...src=0_nl_cme_9

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