Comparison of methods of assessing response of Pagetʹs disease to bisphosphonate therapy

Bisphosphonates have been shown to be effective in suppressing the elevated bone turnover found in Pagetʹs disease of bone. In theory, the major determinants of post-treatment bone turnover are the initial disease activity and the rate of decline in bone turnover with therapy. In the present study, we examined the rate of decrease of alkaline phosphatase and hydroxyproline (expressed as a half-life) and showed this to be superior to percentage changes in bone turnover as a marker of response. The combination of pre-treatment alkaline phosphatase and the alkaline phosphatase half-life and pre-treatment hydroxyproline and the hydroxyproline half-life were the best models to predict post-treatment bone turnover (multiple r = 0.75, r2 = 0.56, p< 0.0001; and r = 0.71, r2 = 0.51, p< 0.0001, respectively). In addition, measurement of the half-lives of these markers of bone turnover may allow prospective changes to be made during treatment so that maximal disease suppression can be achieved.