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Osteoporosis is more than a T-score
By Krupa Doshi, MD, CCD; Leila Khan, MD, CCD; Susan Williams, MD, MS, CCD; Angelo Licata, MD, PhD
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The Endocrine Calcium Clinic within Cleveland Clinic’s Department of Endocrinology, Diabetes and Metabolism published a paper outlining our recommendation that the interval between bone mineral density (BMD) tests should be guided by an assessment of clinical risk factors and not just T-scores.
While the criteria for screening patients with BMD measurement are well established, the guidelines for repeat testing are scarce. A study published by Gourlay et al. in the New England Journal of Medicine conveyed the message that repeat scanning of older women with normal or near-normal bone density (T-scores) may be deferred for several years. The article emphasized the T-score as the only criterion for disease and follow-up scanning.
We found the study’s findings overly simplistic and quite concerning because physicians, patients and the media may misinterpret the information as a widely applicable guideline for all patients regardless of age, gender and clinical history.
There is no doubt that BMD measurement by dual-energy X-ray absorptiometry (DXA) is the gold standard to diagnose primary osteoporosis and assess fracture risk. Few clinicians would doubt the relationship between T-score and patients’ risk for osteoporotic fracture. But this is not the whole story. Osteoporosis — or the risk for fragility fracture — is more than a T-score. Clinicians must recognize the fact that a clinical situation may drive the fracture risk, which may be high even in the presence of normal BMD measurements.
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It is important to recognize the fact that DXA technology — at present the best available tool to diagnose osteoporosis — has its limitations. A single measurement in time does not easily predict the presence of structural weakness or future fracture.
Bone strength and resistance to fracture are functions of both bone density and “bone quality.” Bone quality is a concept that extends beyond bone density to include a number of properties of the bone that make the skeleton resist fracture, such as its microarchitecture, accumulated microscopic damage and the collagen structure. Intercurrent illnesses, changes in bone turnover, and medication such as glucocorticoids and aromatase inhibitors are some factors that can influence the composition and structure of the bone without actually making it thin or porous or affecting its density.
Therefore, a single “good/normal” baseline T-score may not always predict the risk of fracture accurately — which means that BMD by DXA cannot measure bone strength in its entirety, since it cannot detect all of the qualitative changes in bone strength. Apropos to the Gourlay paper, a normal score when viewed in a patient’s clinical context may very well demand repeated DXA measurements more often than the authors suggested.
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In summary, while T-score definitions of osteoporosis can be useful to establish the diagnosis of osteoporosis and estimate the prevalence of this disease in the general population, they should not be used as the sole determinant to make treatment decisions in an individual.
Clinicians also must consider patients’ clinical context at presentation to avoid missing windows of opportunity for intervention when it would matter most — that is, before fractures develop.
The authors are all specialists in the Endocrinology & Metabolism Institute’s Endocrine Calcium Clinic within the Department of Endocrinology, Diabetes and Metabolism. Krupa Doshi, MD, and Leila Khan, MD, are endocrinologists with a special interest in calcium and metabolic bone disorders. Susan Williams, MD, is an internist and metabolic specialist with expertise in metabolic bone diseases. Dr. Licata is a retired endocrinologist and former clinic member.
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