Bone densitometry: a new, highly responsive region of interest in the distal forearm to monitor the effect of osteoporosis treatment.

The bisphosphonates have been introduced as alternatives to hormone replacement therapy (HRT) for the treatment and prevention of postmenopausal osteoporosis. The expected increasing application in at clinical practice demands cost-effective and easily handled methods to monitor the effect on bone. The weak response at the distal forearm during antiresorptive treatment has restricted the use of bone densitometry at this region. We describe a new model for bone densitometry at the distal forearm, by which the response obtained is comparable to the response in other regions where bone densitometry is much more expensive and technically complicated. By computerized iteration of single X-ray absorptiometry forearm scans we defined a region with 65% trabecular bone. The region was analyzed in randomized, double-masked, placebo- controlled trials: a 2-year trial with alendronate (n = 69), a 1-year trial with ibandronate (n = 141) and a 2-year trial with HRT (n = 121). Bone mineral density (BMD) at the distal forearm revealed a highly statistically significant dose-related response and increased 3-5% per year with 2.5 mg ibandronate, 10 mg alendronate or HRT, whereas the decrease in the placebo groups was 1-3% (p<0.001). The response at the distal forearm was similar to the response at the lumbar spine and hip. In conclusion, trabecular bone at the distal forearm is as responsive to antiresorptive treatment as trabecular bone in other skeletal regions. Bone densitometry at the new region of interest in the distal forearm has comparable performance characteristics to more expensive and technically demanding methods. The method is more accessible clinically and has potential as an alternative for monitoring bone mass changes during antiresorptive treatment.