musculoskeletal and connective tissue disorders
Osteoporosis
Diagnosis of Osteoporosis
Dual-energy x-ray absorptiometry (DXA) X-rays (generally done, but not diagnostic) Although low bone mineral density (and the associated increased risk of fracture) can be suggested by x-rays, it should be confirmed by a bone mineral density measurement. Typically DXA is used; quantitative CT scanning can produce similar bone mineral density measurements but is not widely available. Bone mineral density should be measured using DXA scan to screen people at risk, provide a quantitative measure of bone loss, help predict the risk of fracture, and monitor those undergoing treatment ( Diagnosis references ). In a DXA scan, the target areas, typically the spine and one or both hips, are imaged using x-rays of high and low energy (hence the term "dual energy"). The difference in attenuation between high and low energy beams is a reflection of bone mineral content. The bone mineral content divided by area of bone (also measured in the DXA scan) is the bone mineral density in g/cm If the spine or a hip is not available for scanning (eg, because of hardware from prior total hip arthroplasty), the distal radius can be scanned (called "1/3 radius" on the DXA scan report). The distal radius should also be scanned in a patient with hyperparathyroidism because this is the most common site of bone loss in hyperparathyroidism. DXA results are reported as T-scores and Z-scores. corresponds to the number of standard deviations that the patient's bone mineral density differs from the peak bone mass of a healthy, young person of the same sex and race/ethnicity. The World Health Organization establishes cutoff values for T-scores that define osteopenia and osteoporosis ( Diagnosis references ). A T-score < -1.0 and > -2.5 defines osteopenia. A T-score ≤ -2.5 defines osteoporosis. The Z-scorecorresponds to the number of standard deviations that the patient's bone mineral density differs from that of a person of the same age and sex and should be used for children, premenopausal women, or men < 50 years. If the Z-score is ≤ -2.0, bone mineral density is low for the patient's age and secondary causes of bone loss should be considered. ADXA scan is recommendedfor the following patients: All women ≥ 65 years Women between menopause and age 65 who have risk factors, including a family history of osteoporosis, a low body mass index, and use of tobacco and/or medications with a high risk of bone loss (eg, corticosteroids, aromatase inhibitors) Patients (men and women) of any age who have had fragility fractures Patients with evidence on imaging studies of decreased bone mineral density or asymptomatic vertebral compression fractures incidentally noted on imaging studies Patients at risk of secondary osteoporosis Current central DXA systems can also assess vertebral deformities in the lower thoracic and lumbar spine, a procedure termed vertebral fracture assessment (VFA). Vertebral compression deformities in the absence of trauma, even those clinically silent, are diagnostic of osteoporosis and are predictive of an increased risk of future fractures. VFA is more likely to be useful in patients with height loss ≥ 3 cm. If the VFA results reveal suspected abnormalities, x-rays should be done to confirm the diagnosis. The need for Antiresorptive medications is based on the probability of fracture, which is related to DXA results as well as other factors. The Bones show decreased radiodensity and loss of trabecular structure but are inadequate for diagnostic purposes. However, x-rays are important for documenting fractures resulting from bone loss. Loss of vertebral body height and increased biconcavity characterize vertebral compression fractures. Thoracic vertebral fractures may cause anterior wedging of the bone. Vertebral fractures most commonly occur at the mid-thoracic level when due to osteoporosis ( Diagnosis references ). Vertebral fractures above the mid-thoracic region should raise consideration for malignancy or trauma as the etiology. X-rays of the spine to look for asymptomatic vertebral fragility fractures should be considered in older patients with severe back pain and localized vertebral spinous tenderness and in patients who report > 3 cm height loss. In long bones, although the cortices may be thin, the periosteal surface remains smooth. Corticosteroid-related osteoporosis, called glucocorticoid-induced osteoporosis (GIOP), is most likely to cause vertebral compression fractures but may also cause fractures at other sites where osteoporotic fractures are common ( Diagnosis references ). Hyperparathyroidism can be differentiated when it causes subperiosteal resorption or cystic bone lesions (rarely). Osteomalacia may cause abnormalities on imaging tests similar to those of osteoporosis. Two metabolic bone diseases decrease bone mass: osteoporosis and osteomalacia. Inosteoporosis,bone mass decreases, but the ratio of bone mineral to bone matrix is normal. Inosteomalacia,the ratio of bone mineral to bone matrix is low. metabolism (see Vitamin D Deficiency and Dependency ). Osteomalacia can be caused by disorders that interfere with Osteomalacia should be suspected if the patient has bone pain, recurrent rib or other unusual fractures, and thevitamin Dlevel is consistently very low. To definitively differentiate between the two disorders, clinicians can do atetracycline-labeled bone biopsy, but this is rarely warranted. An evaluation for secondary causes of bone loss should be considered in a patient with a Z-score ≤ -2.0. Laboratory testing should usually include the following: Serum calcium, magnesium, and phosphorus 25-Hydroxyvitamin Dlevel Liver tests, including testing for a low alkaline phosphatase (hypophosphatasia) Intact PTH level ( Hyperparathyroidism ) in men ( Diagnosis ) 24-hour urine for calcium and creatinine (hypercalciuria) Other tests such as thyroid-stimulating hormone or free thyroxine to check for Diagnosis , measurements of urinary free Patients with weight loss should be screened for gastrointestinal disorders (eg, Diagnosis , Levels of fasting serum C-telopeptide cross-links (CTX) or urine N-telopeptide cross-links (NTX) reflect increased bone resorption. However, the reliability of the assays vary, which complicates their utility for routine clinical care. Studies suggest that elevated levels of CTX and NTX may be helpful in predicting fracture risk in an untreated patient, monitoring response to antiresorptive therapy, and determining the timing of a drug holiday ( Diagnosis references ). In patients on antiresorptive therapy, levels should be markedly suppressed. 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