Catherine Burt Driver, MD, is board certified in internal medicine and rheumatology by the American Board of Internal Medicine. Dr. Driver is a member of the American College of Rheumatology. She currently is in active practice in the field of rheumatology in Mission Viejo, Calif., where she is a partner in Mission Internal Medical Group.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
How often should DXA scans be repeated to monitor treatment?
The frequency of monitoring osteoporosis treatment using DXA scans is highly controversial. Some doctors recommend DXA scanning at one- to two-year intervals to monitor changes in bone density during treatment. But recent scientific evidence questions the usefulness of such interval monitoring. Reasons why repeating bone density scans is extremely tricky include:
Bone density changes so slowly that the changes may
be smaller than the measurement error of the machine. In other words, repeat
DXA scans cannot distinguish between a "real" increase in bone density or a
mere variation in measurement from the machine itself. Typically, BMD changes
1% per year, which is less than the error of a DXA machine (usually in the range of
3%). Changes of less than 2%-4% in the vertebrae and 3%-6% at the hip from
test to test can be due to the precision error of the method.
Whereas the real purpose of prescription osteoporosis treatment is to
decrease future bone fractures, there is no good correlation between increases
in bone density as measured by DXA with decreases in fracture risks with
treatment. There are multiple examples of this in recent clinical studies. For
example, the improvement in BMD only accounted for 4% of the reduction in spine
fracture risk with raloxifene (Evista), 16% of the reduction in
spine fracture risk with alendronate (Fosamax), and 18% of
the reduction in spine fracture risk with risedronate (Actonel, Atelvia). Thus, improvement in BMD does not indicate the
amount of the antifracture benefit of osteoporosis medication. Prescription
medication may decrease a person's risk of fracture even when there is no
apparent increase in BMD. Physicians and nonphysicians alike are often
surprised to learn this information!
Even if the DXA scan shows continued deterioration in
bone density during treatment, no research data exists demonstrating that
changing a medication, combining medications, or increasing medication doses
will be safe and helpful in decreasing the future risk of fractures compared
to just continuing the same medication.
Even if a person's bone density deteriorates during
treatment, it is quite likely that the person would have lost even more bone
density without treatment.
Recent research has
shown that women who lose bone density after the first year of menopausal
hormone therapy will gain bone density in the next two years, whereas women who
gain in the first year will tend to lose density in the next two years of
therapy. Therefore, bone density during treatment naturally fluctuates and may
not be indicative of the fracture protection of the medication.