Predicting subsequent bone density response to intermittent cyclical therapy with etidronate from initial density response in patients with osteoporosis

We investigated whether an increase in lumbar spine bone mineral density (L S BMD) at 6 months or at 12 months could predict the response to intermitte nt cyclical therapy (ICT) with etidronate, defined in one of two ways: (i) an increase in LS BMD at 24 months (improvement) or (ii) an increase in LS BMD greater than or equal to 0.028 g/cm(2) (significant improvement). The l atter is a precision term calculated from test-retest values for LS BMD in osteoporotic patients. Two hundred and forty-seven patients (32 men; 5 prem enopausal and 210 postmenopausal women) were followed for 24 months by dual -energy X-ray absorptiometry (DXA) and were not taking estrogen, calcitonin or fluoride during treatment with ICT-etidronate. One hundred and fifty pa tients had a LS BMD measurement after 6 months of treatment with ICT-etidro nate and 205 patients had one at 12 months. Baseline characteristics (mean; SD) were as follows: age, 66;11 years; years since menopause, 21;10; number of vertebral fractures at baseline, 0.87;1.26; LS BMD T-score, -2.8;1.2. A fter 24 months of treatment with ICT etidronate, 81% of the patients had an improvement, and 55% had a significant improvement at the LS. Only 6% sign ificantly lost bone (loss of 0.028 g/cm(2) or more). The mean percent chang e from baseline in LS BMD was 5.1% (95% confidence interval 4.2% to 6.0%). The results for men and postmenopausal women were similar to those for the entire group. Accuracy and sensitivity were marginally, but not significant ly, higher when response was predicted using 12 month versus 6 month LS BMD measurements. The positive predictive values of improvement at 6 or 12 mon ths were 89% and 90% respectively for improvement at 24 months, and 66% and 68% for significant improvement at 24 months. Identification of nonrespond ers was less successful and similar at 6 months and 12 months. Forty percen t and 39% of the patients, who had no improvement at 6 or 12 months respect ively, also had no improvement at 24 months, i.e., were true negatives, whi le 77% and 71% had no significant improvement at 24 months. The results may reflect slow response in a small subgroup of patients rather than nonrespo nse; however, no response at 1 year might identify patients whose rate of r esponse is sufficiently slow that alternative therapy is justified. These d ata demonstrate a good response rate to ICT-etidronate and may help reduce the need for follow-up BMD measurements in those who show an early improvem ent.