DESTIN, FLA. — A lack of increase in bone mineral density does not necessarily indicate a failure of antiresorptive therapy for osteoporosis, and is not a reason to switch a patient's drugs, Dr. Michael McClung said at a rheumatology meeting sponsored by the Virginia Commonwealth University.
A sizeable proportion of patients on antiresorptive therapy do not have an increase in their bone mineral density (BMD), and some actually experience a decrease, he said. “Patients need to be told up front that these are not bone density-building drugs—they are designed to prevent bone loss and preserve what is there.”
Nor do changes in bone density completely predict future fracture risk, according to a study cited by Dr. McClung, director of the Oregon Osteoporosis Center, Portland. Osteoporosis treatments increase BMD and reduce fracture risk, but even those women with no increase in density experience protection from fracture. “This suggests that most of the reduction in fracture risk is due to something else besides increasing bone density,” he said.
Markers of bone turnover are also an imperfect way to predict future fracture risk, Dr. McClung said. Patients who respond usually have quick and observable changes in their markers, but attempting to use markers to monitor treatment response in individual patients is difficult because of the imprecision of current assays.
Nonresponse can only be identified by deterioration of skeletal health while on treatment. This deterioration is usually defined as a true decrease in BMD, but in clinical trials, it's very uncommon. With estrogen or alendronate, nonresponse occurs in less than 3% of patients. In clinical practice however, bone loss may be more common (8%–10%) due to noncompliance, poor bioavailability, and other medical issues that affect bone health.
“Don't overinterpret any changes, or lack of changes, you see when you monitor patients,” said Dr. McClung. “The main reason to follow BMD after starting therapy is to identify those patients who continue to lose bone mass. Seeing no change or even a decrease in bone density is a signal to review dosing and compliance, and to take another look at any other medical circumstances that could be affecting bone health.”
It is not even possible to monitor treatment response with some agents, like calcitonin, which have very small effects on BMD or markers, Dr. McClung said.