How should a DEXA scan be used to evaluate bisphosphonate therapy for osteoporosis?
Recommendations from others
Guidelines on monitoring the clinical response to osteoporosis therapy with DEXA are available from numerous groups ( TABLE ). In clinical practice, it is common for a BMD difference of 3% to 5% at the spine or 4% to 6 % at the hip to be considered clinically significant.13
TABLE
Recommendations on monitoring the clinical response to DEXA in osteoporosis therapy
| Organization | Method used to formulate responses recommendation | Recommendations for monitoring treatment to anti-resorptive therapy |
|---|---|---|
| AHRQ Evidence Report (Osteoporosis in Postmenopausal Women)14 | Systematic review | Advises against repeating bone density tests within the first year of treatment. Insufficient evidence to determine whether repeating tests 2 years after starting therapy is useful |
| American Association of Clinical Endocrinologists13 | Rating scheme (Statement not rated) | Yearly for 2 years and if bone mass has stabilized, follow-up measurements are recommended every 2 years |
| Canadian Panel of Clinical Densitometry15 | Not stated | Repeat scan should be considered after 1 to 3 years if concerned about progressive bone loss or with new intervention |
| Institute for Clinical Systems Improvement1 | Not stated | Controversy exists as to whether follow-up testing is necessary in all patients, but if performed, it should be done after 1 to 2 years of therapy |
| National Institute of Health16 change | Expert consensus | Monitoring has not been shown to improve compliance. Physicians should not stop or therapies because of modest bone density loss |
| National Osteoporosis Foundation6 | Expert consensus | Recommended 1 to 2 years following initiation of therapy |
| North American Menopause Society17 | Expert consensus | Monitoring before 2 years of treatment would not be useful |
| Osteoporosis Society of Canada18 | Not stated | Suggests at least 1 follow-up measurement is necessary. Central bone densitometry 1 to 2 years following initiation of bisphosphonate therapy. For patients receiving hormone therapy, repeat BMD is recommended at 2 to 4 years |
| University of Michigan19 | Evidence rating scheme | For most persons an interval of >2 years between DEXAs provides the most meaningful information |
If follow-up is needed, rescan in 2 to 3 years
Ann B. Gotschall, MD
Baylor College of Medicine, Houston, Tex
Rates of vertebral and hip fractures are significantly reduced by alendronate and risedronate, making them important in the prevention and treatment of osteoporosis. Despite controversies over the timing and necessity of monitoring bisphosphonate therapy with DEXA scans, they may be useful clinically if their limitations are recognized. It is necessary to wait 2 to 3 years to repeat the DEXA after initiating therapy to account for the slow rate of change of bone density and compensate for the regression-to-the-mean phenomenon seen in clinical trials.
If after 2 or 3 years the bone density remains stable or has increased, reassurance can be given that fracture risk has decreased. If bone density has decreased more than the LSC, consider the following questions. Is the medicine is being taken first thing in the morning on an empty stomach? Is weight-bearing exercise performed routinely, tobacco avoided, and caffeine limited? Is the patient continuing adequate calcium and vitamin D supplements? The physician should also consider secondary causes of osteoporosis, such as hyperthyroidism and hyperparathyroidism.
