Changes in QUS and BMD measurements with antiresorptive therapy: A two-year longitudinal study

There is lack of consensus on whether quantitative ultrasound (QUS), measur ements can be used to monitor response to therapy. The aim of this 2-year l ongitudinal study was to assess, whether calcaneal QUS measurement variable s respond to antiresorptive therapy and whether these measurements display adequate long-term precision to be useful for monitoring purposes. The stud y population consisted of 195 postmenopausal women divided into three group s: Group 1: 39 women treated with antiresorptive therapy who commenced trea tment at baseline; Group 2: 25 women treated with antiresorptive therapy wh o had been on treatment for at least 2 years at baseline; Group 3: 131 wome n who did not taken estrogen, bisphosphonates, or calcium during the 2-year study period. Subjects had baseline and 12 and 24 months follow-up BMD mea surements at the lumbar spine (LS), femoral neck (FN), and total hip (THIP) , and calcaneal QUS measurements of broadband ultrasound attenuation (BUA) and speed of sound (SOS). BUA and SOS were combined to provide an estimate of heel BMD (Est heel BMD). For women in Group 1, all BMD and QUS measureme nt variables increased significantly from baseline after 2 years of treatme nt. For women in Group 2, only THIP BMD and BUA increased significantly aft er 2 years and the changes were less than those observed in Group 1, women. The overall treatment effect for each measurement variable, defined as the difference in the mean absolute changes between Groups I and 3 after 2 yea rs, was 0.08, 0.03, and 0.04 g/cm(2) for LS, FN, and THIP BMD, and for BUA, SOS, and Est heel BMD it was 5.8 dB/MHz, 13.1 m/sec, and 0.05, g/cm(2), re spectively. When the overall treatment effect was expressed in T-score, uni ts, the effect was greatest for LS BMD (0.65 T-score units), and lowest for FN BMD (0.31 T-score units). QUS measurement variables yielded intermediat e values of 0.43- 0.52 T-score units. The average least significant change (1,K) was 0.38 T-score units for BMD measurements, whereas the LSC for QUS measurements was three times greater at approximately 1.20 T-score units. N inety-four percent of the women in Group 1 showed changes in LS BMD that ex ceeded the LSC after two years, while the percentage was lower for the othe r measurement variables ranging from approximately 60% for FN BMD, SOS, and Est heel BMD to 50 % for THIP BMD. A lower percentage of women in Groups 2 and 3 displayed changes that exceeded the LSC for both BMD and QUS measure ment variables. Changes in all QUS variables were significantly correlated with changes in LS BMD, with correlation coefficients ranging from 0.26 to 0.40. In conclusion, calcaneal QUS measurement variables were found to show a highly significant response to antiresorptive therapy. However, the prec ision of QUS measurements was not good enough to allow QUS to be used for m onitoring response to treatment. Future improvements in the precision of ca lcaneal QUS measurements, are required to increase the utility of QUS for m onitoring purposes.