Thursday, August 23, 2012

DJD and BMD

Degenerative joint disease (DJD) of the lumber spine (in addition to compression fractures, scoliosis, and aortic calcification) often leads to misinterpretation of bone density (DXA) scans and the under-diagnosis of osteoporosis. In a study published in Osteoporosis International (Tenne et al., 2012), researchers reported: "Clinical use of spinal BMD [bone mineral density] measurements become increasingly problematic with age, and in fact difficulties in accurately assessing spinal BMD may already be apparent soon after menopause. Consequently, recommendations suggest that the hip is a more reliable site for BMD measurement particularly because while rate of bone loss in the spine and distal radius appears to cease in the elderly, this does not apply to the hip where continuous bone loss is seen with advancing age."

"In the most recent recommendations from the International Society for Clinical Densitometry (ISCD), it is recommended that all vertebrae (L1-L4) are included in the average values used for diagnosis compared to the previously most used L-2-4. Furthermore, it is also suggested that a vertebra that is not possible to evaluate because of local structural changes or a more than 1.0 T-score difference compared to adjacent vertebrae, should be excluded." But even with these recommendations "falsely elevated spinal BMD with advancing age is an important reason for underdiagnosis and insufficient initiation of osteoporosis medication, and it also allows for misinterpretation of drug effects during monitoring of therapy."

Results from this study indicate that "by choosing the more superior vertebrae for BMD measurements, a large proportion of degenerative changes potentially distorting the diagnostic score would be excluded." By measuring the density of  L1-L2 instead of L1-L4, the study found 20% more cases of osteoporosis (29% more at 10-year follow-up) and 37% more when subjects without degenerative changes were measured. The authors argue that these findings are clinically important especially in patients "around the age of 75 since it has been suggested that in the elderly, the hip should be used to diagnose osteoporosis by BMD measurement." According to the researchers, because the rate of bone loss in the hip is less than that in the spine, using the hip as the focus for diagnosing osteoporosis in the elderly does not compensate for those missed (osteoporosis) diagnoses using the standard spine BMD (L2-L4). The authors argue that it is of more value to use the L1-L2 measurement (in conjunction with an estimation of degenerative manifestations) for identifying patients in need of therapy. "Since fractures seconday to osteoporosis are an extensive source of human suffering and cost to society, early diagnosis is essential for preventive treatment and relief on an increasingly burdened health care due to an ageing population."

A surprising finding from this study was that "in women without apparent degenerative changes, spinal bone mass appears to remain stable from age 75 to 85 years" and "the absence of bone loss is not explained by pharmacotherapy." I thought this particulary encouraging.

Tenne, M., F. McGuigan, J. Besjakov, et al. 2012. Degenerative changes at the lumbar spine--implications for bone mineral density measurement in elderly women. Osteoporosis Int 10.1007/s00198-012-2048-0.

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