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Dr. Kleerekoper has posted about DXA issues before. Now it is my turn.
I review the previous DXA of all patients that come to see me regarding
osteoporosis and bone disease. I continue to be surprised by the range in
quality of interpretations I see. The DXAs below were from the same patient
conducted at an outlying facility between 2008 and 2010.
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Images courtesy of Thomas Repas,
MD |
Despite the poor quality of the images, it is obvious that the levels on
one study were not the same on the other. What is L1-L2 on one
study is L3-L4 on the other. Technologists are human as we all are
and humans occasionally make mistakes. Nevertheless, it is the responsibility
of the interpreting physician to review and catch such an error if it
occurs.
The interpretation was: Mild to moderate osteopenia with mild to
moderately increased fracture risk. The mistake in the labeling of the
lumbar spine was missed I wonder if the images were reviewed at all.
There is no such thing as mild to moderate osteopenia. If
the T-score is between -1.0 and -2.5, the diagnosis is osteopenia. Indeed, the
preferred term per the International Society of Clinical Densitometry (ISCD) is
low BMD. When I calculated the patients estimated 10year fracture risk
per the WHO FRAX calculator, her risk for major osteoporotic fracture and of a
hip fracture were not increased beyond that of other 50-year-old women.
Poor quality DXA interpretations are not uncommon and in some facilities
they even appear to be the rule rather than the exception. I remember another
case of a 17-year-old who was diagnosed with osteoporosis and begun on oral
bisphosphonate because of a Wards triangle T-score of less than -2.5. She
had no history of skeletal fragility or fracture. DXA was ordered because she
had been on Depo-Provera for several months.
When I reviewed the images myself, my interpretation was bone mass
within the expected range for age. Per the guidelines of the ISCD, Wards
triangle should never be used in determination of low BMD or osteoporosis. I
advised her to stop the bisphosphonate as there was no indication for it.
In pre-menopausal females, we use Z-scores, not T-scores in the
evaluation of BMD. A Z-score of less than -2 would be bone mass below the
predicted range for age. This young womans Z-score was greater than -2; therefore she was normal. In women who are pre-menopause as well as men
younger than age 50, osteoporosis cannot be diagnosed unless there is evidence
of skeletal fragility no matter what the T-score or Z-score is.
I have forwarded copies of the ISCD Position Statement to centers which
have had problems in performing and interpreting DXA. Thus far, I have received
no response. I have seen no change in the quality of their DXA. This is a
problem particularly for primary care providers who may not understand the
intricacies and limitations of DXA. They may make treatment decisions based on
DXA interpretations that are not accurate.
I strongly believe in certification of physicians and technologists by
the ISCD. If more physicians and technologists were certified and trained in
performing and interpreting DXA, errors such as these would be much less
common.
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To my recollection, non-invasive measurement of bone mineral density
began several decades ago with single photon absorptiometry of the radius. At
that time of the publication of the 1994 WHO guidelines, more of the data were
based on forearm measurements than on spine or hip measurements. There is no
doubt that BMD of the spine and hip provides a better prediction of major
fragility fracture risk than does measurements at the forearm. That does not
mean that forearm BMD should be ignored entirely since it has been documented
to predict future spine or hip fractures. Remember, the Colles (wrist) fracture
is the earliest clinical manifestation of postmenopausal osteoporosis. It is
also the most missed fracture in terms of making a clinical diagnosis of
osteoporosis.
The one-third radius site is the only forearm site that is approved for
reimbursement, but measurement at the ultra–distal radius site can easily
be measured during a forearm DXA study without adding to the cost or time taken
to conduct the test. (Why does my field continue to use unnecessary
terminology? Why not simply call it the distal radius site?) In my practice, I
always order spine, hip and forearm BMD — there are some circumstances
where forearm BMD is most helpful.
- Primary hyperparathyroidism: While this is a systemic disease
affecting the entire skeleton, the lowest BMD is most often the forearm, which
may be the only site at which BMD is less than –2.5. In this case, the result
should influence the decision regarding surgical cure of primary
hyperparathyroidism (PHPT).
- Hyperthyroidism: The effect of thyroxine on the skeleton is similar
to that of parathyroid hormone, but at the kidney the effect is quite
different. Hypercalcemia is seen in hyperthyroidism, but it is usually
accompanied by a normal or elevated serum phosphate as opposed to the low serum
phosphate in hyperparathyroidism. Rumor has it that one of Friedrich Daniel von
Recklinghausen's original 13 cases of osteitis fibrosa was, in fact, Iod
Basedow's disease (better known now as Grave's disease). I am not suggesting that patients with hyperthyroidism need
a BMD study, but if you do routinely perform forearm density and it is the
lowest of the three measured sites — thyroid function tests are in
order.
- Scoliosis: I am never comfortable interpreting BMD of the spine in
patients with scoliosis. The more pronounced the scoliosis, the less
comfortable I am. Not only are there technical difficulties with spine DXA in
scoliosis, but the loading of the vertebral bodies is quite different from
normal, and we simply do not know the relationship between spine BMD and
fracture risk in this condition. If scoliosis is detected clinically before the
study is ordered, omit the spine measurement and measure the forearm. If
scoliosis is detected by the technologist performing the density study, the
spine study should be completed and a forearm study should also be done. Three
sites are better than two — two sites are better than one.
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One of the most difficult challenges of clinical endocrinology practice
is inspiring our patients to adhere to recommendations for dietary
modification, lifestyle change and pharmacotherapy.
The traditional information-based approach focuses on educating the
patient so that they will understand why and how to change. The physician told
the patient what was to be done and the patient was expected to follow this
advice without question. Those who did not follow recommendations were
labeled non-compliant. Some providers use scare tactics in an
attempt to frighten or bully patients into complying. Not surprisingly, this
approach usually failed.
More recently, researchers have evaluated what successfully motivates
people to change. This has led to a patient-centered, goal-oriented model of
provider-patient interaction, known as motivational interviewing. This
technique has been shown to be effective in improving adherence to
recommendations for chronic disease management including behavioral
modification and pharmacotherapy.
Motivational interviewing is based on three basic assumptions:
Collaboration, evocation, and autonomy. By understanding and respecting these
assumptions, practitioners establish rapport, reduce resistance, support
autonomy, and elicit change talk with the ultimate goal of
improving clinical outcomes.
Patients appreciate when we try to understand their situation instead of
simply telling them what to do. By showing that we value their autonomy,
understand that it is their choice and are not trying to manipulate them into
change, they are more likely to consider following our recommendations. By
exploring ambivalence and barriers for adherence to therapy, we have a better
understanding of why non-adherence may occur and how to avoid it. Finally, by
involving the patient in developing their treatment plan, they have greater
ownership and as a result are more likely to follow through.
Times have changed and I am glad they have.
Butterworth. J Manag Care Pharm. 2008;14:S21-S25.
Rollnick S. Motivational Interviewing in Health Care: Helping
Patients Change Behavior. New York: Guilford Press; 2007.
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