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.
Bone density vs. bone quality
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.
The following two scenarios illustrate this point:
- A 55-year-old postmenopausal woman who has received inhaled steroids and pulse therapy with oral steroids for most of her life for asthma presents with a humerus fracture after falling off a curb. Her lowest T-score is –0.5. This patient has a normal BMD by T-score. However, she may be classified as having clinical osteoporosis by virtue of the presence of a fragility fracture, and chronic steroid exposure indicates that she may continue to have an increased risk of fracture. Here, a T-score alone misclassifies the patient as having a normal BMD. However, her clinical risk factor assessment reclassifies her as having osteoporosis and warrants the use of pharmacological therapy to prevent further bone loss and more frequent DXA testing.
- A 40-year-old woman presents with T- and Z-scores of –1.0 and –1.9, respectively, at the hip and multiple rib fractures that developed in the couple of years after she underwent a malabsorptive bariatric procedure and lost more than 100 pounds. All patients who have undergone a surgical weight loss procedure should undergo routine screenings for metabolic bone disease. The patient reports normal menstrual cycles and no family history of osteoporosis. Her blood work indicates severe secondary hyperparathyroidism from very low vitamin D levels and hypocalciuria despite taking daily over-the-counter calcium and vitamin D supplements. After aggressive oral repletion with calcium salts and cholecalciferol, her vitamin D and urine calcium levels normalized. Repeat BMD testing 12 months later showed an 8 percent increase in hip bone density. This case illustrates the fact that not all low T-scores indicate “osteoporosis.” Other factors, such as osteomalacia from vitamin D and calcium deficiency, also can have a profound effect on bone density. Recognition and management of these conditions will alter the frequency of BMD testing to detect a clinically meaningful change.
Opportunities for prevention
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.