Osteoporosis: Diagnosis and Managements _ _____________________________________________________
The key to diagnosis is a thorough history and physical examination, followed by bone measurement tests. Because low BMD may indicate metabolic bone disease other than osteoporosis (e.g., hyperparathyroidism or osteomalacia), it should not be used as the sole indicator of osteoporosis [20]. Healthcare professionals should also ask about other risk factors for osteoporosis, as well as any family history, pain or tenderness in bones or joints, recent broken bones, current and recent past medication use, and level of physical activity. For men, physicians should inquire about changes in libido. On exam, it is important that height is measured and compared with results from past measurements. There also should be a focus on evidence of old fractures during a skeletal survey, as previous fractures often may signal the presence of osteoporosis or a metabolic abnormality. If suspicion for osteoporosis is high, bone measurement testing should follow. Patient D has a full chemistry panel including calcium and phosphorus, liver function tests, thyroid function tests, and a complete blood count (CBC). All are within normal limits. Normal values should not be unexpected in patients with osteoporosis, as this is often the case. Because suspicion remains high for osteoporosis, Patient D must undergo bone mineral density testing. Although the patient wishes to have an x-ray, simple x-rays would not be helpful here unless one is trying to rule out a fracture or other structural cause of the low back pain. BONE DENSITY MEASUREMENT TESTS There are several ways to determine bone mineral density, and each diagnostic tool may identify a different population with osteoporosis. Bone measurement tests include DXA of the hip, spine, or wrist; quantitative ultrasound of the heel; spinal CT; radiographic absorptiometry; and MRI. These tests are most useful when they will have an effect on clinical decision making. That is, physicians should have a plan before they order a test and anticipate how the test result will affect their management of the patient. There is considerable debate among the several disciplines that perform bone density studies. Osteoporosis clinics using DXA have their preferences, while radiologists performing CT scans or MRI may have different ideas. The spectrum of available tests is outlined here, but most authorities now prefer DXA [20; 31; 34; 35; 36]. The types of studies performed and their appropriate follow-up times continue to be investigated at many centers. For additional information, one may review the Official Positions of the ISCD [33]. Dual-Energy X-Ray Absorptiometry The most commonly used BMD assessment is DXA, which may be done either at central or peripheral (pDXA) sites. DXA uses two distinct beams of x-ray photons. The amounts of each x-ray beam that pass through bone and soft tissue are compared to estimate the bone density. DXA measures the sum of cortical and trabecular bone and can detect as little as 2% bone loss. Central DXA measures BMD at the spine, upper femur, and hip, whereas pDXA measures BMD at the heel, finger, and forearm. Measurement of hip BMD represents a good approach because there is less soft tissue and other artifacts compared to
other sites. Individuals with osteoporosis have a greater risk of fractures in the hip and spine, which can lead to longer recovery time, greater pain, and permanent disability [23; 37]. These sites also are appropriate for monitoring the effectiveness of therapy, as they are more likely to show an increase in BMD in response to treatment [23]. Be aware, however, that falsely elevated BMD may occur in patients with certain pathologic processes, such as degenerative joint disease, compression fractures, and vascular calcifications. Central DXA is generally preferred over pDXA as it can measure whole body bone mass. It has minimal radiation exposure and may be completed in less than 10 to 15 minutes [37]. Peripheral DXA may be done with portable units in a physician’s office and involves even less radiation than central DXA. It is also less expensive. However, it is less sensitive and less specific and thereby provides less precise T-scores. Moreover, pDXA cannot detect spinal fracture sites. It is most useful at identifying at-risk individuals who may benefit from further BMD testing [23; 37]. Quantitative Ultrasound Quantitative ultrasound is based on the premise that attenuation of sound waves into bone and the speed of sound correlate independently with BMD of the heel. The calcaneus is the primary site of measurement, although this technique also has been used to measure bone mass at the tibia, phalanges, or wrist. It is believed that ultrasound measures changes in bone architecture. Limitations include measure reproducibility (should not be used for monitoring bone changes over time or to evaluate response to therapy) as well as lack of adaptation for various sizes and shapes of heels. It involves no radiation exposure, but it is less sensitive than DXA and does not always correlate with DXA readings. However, some studies have indicated that quantitative ultrasound may predict fractures as well as other measures of bone density [20; 21; 38]. Quantitative Computed Tomography Quantitative CT can measure the lumbar spine, hip, and peripheral sites. In general, the results are less likely to be affected by degenerative spinal changes than spinal DXA scanning. Unlike DXA, quantitative CT allows for assessment of both cortical and trabecular bone. As a result, it can make volume BMD determinations [20]. Trabecular bone, because of its higher rate of turnover compared with cortical bone, is expected to show metabolic changes earlier [39]. The ability of quantitative CT to enable prediction of spinal fracture is equal to that of DXA scanning in postmenopausal women; there is lack of sufficient evidence for fracture prediction in men [20]. The cost and level of radiation exposure are higher (as much as 200 times greater than some other techniques) [20]. In some cases, this results in decreased patient acceptability. Radiographic Absorptiometry Radiographic absorptiometry provides radiologic assessment of the metacarpals and phalanges. It was originally based on a plain film; however, computerized image processing has
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