Normal DXA bone mineral density but frail cortical bone in Turner's syndrome

Abstract

Patients with Turner's syndrome have normal bone mineral density by dual energy X-ray absorptiometry (DXA), but a predisposition for fractures. Quantitative ultrasonography (QUS) measures cortical bone strength. To compare QUS with DXA in patients with Turner's syndrome. Twenty-seven Turner's syndrome patients, aged 21.1 +/- 6.3 years (mean +/- SD), were evaluated by DXA, measuring two-dimensional bone mineral density (BMD), and QUS, measuring speed of sound (SOS) of the radius and tibia. The results were compared to sex- and age-matched (Ctr A, n = 53) and height-matched (Ctr B, n = 34) control groups. Fracture incidence per 1000 women years was 4.76 in Ctr A, 5 in Ctr B and 7.69 in Turner's patients. In Turner's syndrome patients, QUS results were significantly lower than in controls, whereas DXA Z-scores were not different from reference values. Correlation between tibia and radius SOS and height and age in controls (P < 0.0001) was not evident in Turner's syndrome. Oestrogen or growth hormone therapy had no effect on either QUS or DXA parameters. Bone fragility in Turner's syndrome is reflected by low SOS but not by DXA BMD. Low QUS, which assesses the cortical bone only, supports a defect in cortical bone in Turner's syndrome. Lack of SOS correlation with age, height and hormonal therapy in Turner's syndrome suggests a primary bone defect, rather than enhanced resorption of endocrine origin.