Bone Abstracts

Patients with osteoporosis require treatment with therapies that reduce the risk of fracture which at the spine is significantly influenced by bone microarchitecture. Quantitative computed tomography (QCT) and dual X-ray absorptiometry (DXA) allow measurement of bone mineral density (BMD), a known indicator of fracture risk. Trabecular bone score (TBS) is a novel gray-level measurement derived from spine DXA image texture that is related to microarchitecture and associates with fracture risk independent of BMD. Denosumab (DMAb) results in greater gains in BMD than oral bisphosphonates and in a recent study, this greater improvement in BMD was associated with a larger reduction in vertebral fracture with DMAb compared with alendronate (ALN; Nakamura ASBMR 2012). To further characterize the bone response with DMAb and ALN, we compared QCT vBMD, DXA aBMD T-score and TBS from spine scans obtained in postmenopausal women with low BMD. In a randomized, double-blind, double-dummy study, postmenopausal women aged 50–70 years with low BMD at the spine or total hip received DMAb (60 mg S.C. every 6 months), branded ALN (70 mg orally every week) or placebo (Pbo) for 12 months (Seeman JBMR 2010). Lumbar spine (LS) QCT vBMD, DXA aBMD and TBS were measured from scans obtained at baseline and month 12. TBS values at baseline and month 12 were available for 215 women (73 DMAb, 68 ALN, and 74 pbo). At baseline, mean age was 60 and, at the LS, mean vBMD was 90.4 mg/cm³, mean aBMD T-score was −2.4 and mean TBS was 1.234. Overall, vBMD, aBMD and TBS decreased with Pbo; increased or were maintained with ALN; and improved with DMAb compared with both Pbo and ALN. At baseline, TBS was better correlated with vBMD (r=0.42, P<0.001) than with aBMD T-score (r=0.13, P=0.051). TBS% changes did not positively correlate with those in QCT vBMD or DXA aBMD in any of the treatment groups. In postmenopausal women with low BMD, DMAb increased vBMD, aBMD and TBS vs both ALN and Pbo over 12 months. Altogether these results suggest that changes in TBS are not biased by BMD changes. These data support the concept that TBS acquires information not captured by standard bone density and warrant further investigation of the clinical significance of the positive changes in TBS in response to denosumab.