Forearm bone mineral densitometry cannot be used to monitor response to alendronate therapy in postmenopausal women

Alendronate significantly increases bone mass and reduces hip and spine fra ctures in postmenopausal women. To determine whether forearm densitometry c ould be used to monitor the efficacy of alendronate, we examined changes in bone mineral density (BMD) at the forearm (one-third distal, mid-distal, u ltradistal radius) versus changes at the hip (femoral neck, total hip) and spine (posteroanterior and lateral) in a double-masked, randomized. placebo -controlled clinical trial of 120 elderly women (mean age 70 +/- 4 years) t reated with alendronate for 2.5 years. We found that among women in the tre atment group, BMD increased by 4.0-12.2% at the hip and spine sites (all p< 0.001), whereas BMD increased only nominally at the one-third distal radius (1.3%, p<0.001) and mid-radius (0.8%, p<0.05), and remained stable at the ultradistal radius. At baseline, forearm BMD correlated with that of the hi p (r = 0.550,64, p<0.001), femoral neck (r = 0.54-0.61, p<0.001) and poster oanterior spine (r = 0.56-0.63, p<0.001). Changes in radial BMD after 1 yea r of therapy were not correlated with changes in hip and spine BMD after 2. 5 years of therapy. In contrast, short-term changes in total hip and spine BMD were generally positively associated with long-term changes in total hi p, femoral neck and spine BMD (r = 0.30-0.71, p<0.05). Furthermore, long te rm BMD changes at the forearm did not correlate with long-term hip and spin e BMD changes, in contrast to the moderate correlations seen between spine and hip BMD at 2.5 years (r = 0.38-0.45, p<0.01). We conclude that neither short- nor long-term changes in forearm BMD predict long-term changes in ov erall BMD for elderly women on alendronate therapy, suggesting that measure ments of clinically relevant central sites (hip and spine) are necessary to assess therapeutic efficacy.