The World Health Organization defines osteoporosis as having a BMD that is 2.5 standard deviations below that seen in a healthy normal adult. But, in children, whose BMD is continually changing as they grow, there is no accepted definition for osteoporosis. Dr. Rabinovich said that most experts believe that, in children, a fragility fracture (a fracture of trauma) plus evidence of low bone mass constitutes osteoporosis. “Unfortunately, doctors are often left with the ‘I know it I when I see it’ ” approach, she said.
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Explore This IssueJuly 2008
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What’s the best way to measure bone mass? The most commonly used tool is dual energy radiographic absorptiometry (DEXA). Though the use of DEXA has been validated in the adult population, Dr. Rabinovich said that the pediatric software for DEXA “is much more problematic.” Doctors commonly use a T-score to read the results gleaned from the imaging because that’s what’s used for adults. But they should use a Z-score instead, so that the patient’s bone mass is compared to age-adjusted norms. Dr. Rabinovich said that the mistake is all too common.
But even after you have a measure of bone density, she said, “bone density does not mean bone strength.” Bone strength also includes measures of structural properties, geometry, cortical thickness, and the material properties of collagen.
Finally, she addressed “the questions everybody wants answers to”: who to treat, when, and for how long?
Regarding pharmacological treatment, all options have had their share of controversy. Dr. Rabinovich noted that calcitriol was shown to be ineffective. Fluoride, she said, “is fascinating,” because it was shown to increase BMD but ultimately increase the rate of fractures. Parathyroid hormone (PTH) has been used in the adult population, but has not yet been tried in children. “There’s a concern of osteosarcoma risk,” she said, so doctors have been “very hesitant to give it to children.”
Finally, “that leaves us with bisphosphonates,” she said. These agents inhibit bone resorption. A study in the late 1970s showed that this therapy significantly increased BMD in children. However, because bisphosphonates slowly get released from bone, and have a half-life in bone of as much as 10 years, there is some concern about their potential long-term effects. “If girls become pregnant, will their fetuses be exposed?” she asked. Some anecdotal reports of prolonged administration, she added, found that it made bones brittle.
The best treatment strategy is to “start with the basics,” said Dr. Rabinovich. Physicians should recommend calcium supplementation, increased physical activity, and aggressively treat any inflammatory disease. The best source of calcium for children is low-fat dairy products, such as milk, cheese, and yogurt. Other foods that are rich in calcium include sardines, canned salmon, broccoli, and dark, leafy greens.