Bone Densitometry Can Cloud Clinical Picture - of osteoporosis treatment - Brief Article

0 Comments | Family Practice News, August 15, 2000 | by Christine Kilgore

BETHESDA, M.D. -- Bone densitometry has "revolutionized the understanding and prevention of osteoporosis," but it has also confused osteoporosis treatment and monitoring, Dr. Steven R. Cummings said at a meeting on bone densitometry sponsored by the National Institutes of Health.

Using bone densitometry to monitor treatment may mislead physicians about the best course of care, said Dr. Cummings, a professor of medicine, epidemiology, and biostatistics at the University of California, San Francisco.

Physicians have been led to believe that improvements in bone density will lead to a reduced risk of fractures, a presumption that is now well established in medical practice but despite inconsistencies and complexities, he said.

More than a decade ago, results of randomized trials first showed that use of sodium fluoride yielded dramatic increases in bone mineral density (BMD) of the spine but led to no significant decreases in fracture risk because fluoride impaired )one quality, Dr. Cummings said.

In the 1990s, clinical trials of calcium, viamin D, alendronate, raloxifene, and other antiresorptive drugs showed dramatic reductions in fracture risk, despite yielding only small improvements in bone density.

"With all these drugs, we were seeing 50%-60% reductions in fracture risk [but] modest impact on bone density," he said.

For each 1% gain in spinal BMD, the risk of vertebral fracture is reduced by 4%, based on a yet-to-be-published metaanalysis conducted by Dr. Cummings and his associates. But the metaanalysis also suggests that antiresorptive treatment reduces the risk of fracture by an additional 20%-25% that is not due to its effect on BMD.

Bone turnover may weaken bone, and by slowing bone resorption, "you may strengthen bone to a greater degree than you'd expect from improvement in bone density," he said. Densitometry would not detect such an effect.

Densitometry monitoring of patients getting osteoporosis treatment relies on the idea that those who lose BMD aren't adhering to or are not responding to therapy, and that those who lose BMD will continue to lose it unless therapy is changed.

Analyses of data from the 6,400 women in the Fracture Intervention Trial (FIT) of alendronate showed that those who lost hip BMD initially during treatment might have lost more without the drug.

Overall, 18% of women in the FIT trial lost BMD during the first year of treatment with alendronate. But of those who lost less than 4% of BMD in the first year, 67% gained BMD in year 2, with an average improvement of 1%. Also, those who lost more than 4% had a 92% chance of gaining BMD later, with an average gain of 5%. And those who gained more than 8% in the first year were likely to lose BMD in year 2, with an average loss of 1%.

Most importantly, women who lost BMD during the first year of alendronate treatment had a 48% lower risk of fractures than did those who lost BMD while on placebo, Dr. Cummings said.

"I've seen many patients who've had therapies added, stopped, changed, and who've worried because their bone density didn't go the way they expected in the first year," he said. The belief that fracture risk is reduced only when BMD improves is firmly entrenched and hard to dispell.

"If the patient requests [densitometry] and you decide to monitor, then don't base decisions solely on the change in BMD," Dr. Cummings advised in an interview.

Factors like age and body weight are important clinical risk factors, but "it's not easy" to apply them to treatment decisions. "Risk factors are important, but we haven't done our job as researchers yet--to integrate risk factors well with measurement of bone density," he added.