The Dexa Scan or Dual Energy X-Ray Absorptiometry Scan is used to diagnose and to follow Osteoporosis. In theory, when 2 X-ray beams with different energy levels are aimed at the patient’s bones and soft tissue absorption is subtracted out, the Bone Mineral Density can be determined. But, Medicine is not a perfect science and, as with most tests, sometimes the numeric value or perhaps even the interpretation of the numeric value does not tell the whole story.
Bisphosphenates such as Alendronate and the others have been approved to treat Osteoporosis by the FDA, largely by showing improvement in Dexa Scan scores. Unfortunately, some investigators point out that bisphosphenates are industrial chemicals that mostly coat the bones so that when the scan is repeated, a higher number is reported. These drugs have largely not been shown to build bone matrix (bone structure).
And here’s another example why interpretation of the scan can be tricky. A patient of mine recently went to see an Endocrinologist who ordered a Dexa Scan and also ordered x-rays of the spine. The scan results did not meet the numerical criteria for either Osteopenia or Osteoporosis and the patient was told that “everything is fine” on the basis of the score. However, the x-rays were reported by the Radiologist as showing “Anterior Wedging” and “Exagerated Kyphosis”. “Anterior Wedging” means that the normally square shaped vertebra had assumed more of a triangular shape due to the front (anterior) part of the vertebra being squished down on itself. And, “Kyphosis” is the bent-over stance that is most evident in older patients who are losing height. You’ve seen them…little old people walking slowly who can’t keep their heads up because their spines are bent over forwardly. While this was not visually evident in this patient, the astute Radiologist could see it on x-ray and reported it as such.
Now imagine this. Let’s say vertebra is square shaped and it is not gonna collapse on itself and become triangular shaped unless there is loss of bone matrix and the structural integrity in the interior of the bone is weaker. So, if a bone is “thinned out” and it collapses on itself … then perhaps the Dexa Scan is gonna produce a “more dense” reading than it would have if it hadn’t collapsed on itself.
Therefore, my interpretation was that this patient is losing bone matrix and I would not have told this patient that “everything is fine”. I would have counseled this patient on nutrition and the building of bone and I would have had a discussion on management of his impending Osteoporosis, including Bio-Identical Hormone Replacement.
BTW, how many times have you gone to the Doctor and you have been told that “everything is fine” but you come away with a funny feeling inside that everything may not be?
In another post, I will comment on the “normal range” of lab tests and how they are not what you think they are. This is most true in the interpretation of Thyroid Function Tests.
Action to Take: search Osteopenia vs. Osteoporosis, 95% confidence level, standard deviation