Comparative assessment of bone mineral measurements using dual X-ray absorptiometry and peripheral quantitative computed tomography.

A measurement of bone mass is the single most important determinant of future fracture. However, controversy exists as to which technique (dual X-ray absorptiometry (DXA) or peripheral quantitative computed tomography (pQCT), and which site of skeletal measurement (axial vs appendicular) provides the best prediction of fracture risk. The aims of this study were: (1) to determine the ability of pQCT to predict bone mass of the lumbar spine, proximal femur, and distal forearm measured using DXA, and (2) to compare the ability of DXA and pQCT to discriminate prevalent fractures in women with established osteoporosis. One hundred and sixty-five women were studied, including 47 with established osteoporosis (vertebral, hip or Colles' fractures) as well as 118 who had bone mass measurements to assess osteoporosis risk. Each subject had bone mass measured by DXA at the lumbar spine and femoral neck, and at the distal radius by both DXA and pQCT. In women with fractures, bone mass, when expressed as a standardized score, was in general lower using DXA compared with the appendicular skeleton measured using pQCT. Bone mass determinations at all sites were significantly correlated with each other. The highest correlation coefficients were observed within the axial skeleton. In women with fractures, the highest odds ratios were observed at skeletal regions measured using DXA. Likewise, the areas under the receiver-operating characteristic (ROC) curves were comparable at all skeletal regions measured using DXA; and were significantly greater than the areas under the ROC curves for pQCT measurements. In summary, the strongest discriminators of prevalent fractures were measurements using DXA. Measurements of bone mass at the appendicular skeleton, using either DXA or pQCT, were poorly associated with axial bone mass. PQCT has the poorer ability to discriminate persons with fractures, and appears to be less sensitive than measurements using DXA.

Reduced bone mass and fat-free mass in women with multiple sclerosis: effects of ambulatory status and glucocorticoid Use.

Multiple sclerosis (MS) is associated with reduced bone mass and vitamin D deficiency. The underlying pathophysiology of the bone disease is uncertain, however, acute and long-term glucocorticoid use, progressive immobilization, vitamin D deficiency, and possibly skeletal muscle atrophy are likely to be determinants. The aims of this study were to determine (a) whether multiple sclerosis is associated with reduced fat-free mass and (b) whether in patients with multiple sclerosis, ambulation ability or glucocorticoid use is associated with bone mass and/or fat-free mass. Seventy-one female patients with MS were compared with 71 healthy, age-matched female controls. Total body bone mineral content (TBBMC, kg), fat mass (FM, kg), and fat-free mass (FFM, kg) were measured using dual X-ray absorptiometry. Disability status was graded according to the Kurtzke Expanded Disability Status Scale (EDSS) as ambulatory, with or without aide (EDSS score of 0 to 6.5), or predominantly wheelchair bound (EDSS score > 6.5). The patients with MS, when compared to age-comparable controls, had deficits in TBBMC ( approximately 8%, -0.3 +/- 0.1 SD, P < 0.04) and FFM ( approximately 5%, -0.3 +/- 0.1 SD, P < 0.01). Both TBBMC and FFM were negatively associated with EDSS score (r = 0.33, P < 0.01, and r = 0.41, P < 0.01, respectively). Patients with MS who were nonambulatory had even greater deficits in TBBMC and FFM as compared with age-matched controls (-0.6 +/- 0.1 SD, P < 0.01, and -0.6 +/- 0. 1 SD, P < 0.01, respectively). By contrast, as compared with age-comparable controls, ambulatory patients with MS had no deficits in bone mass or soft tissue mass. When compared with ambulatory patients with MS, nonambulatory patients with MS had deficits in TBBMC and FFM (P < 0.01 and P < 0.01, respectively). The difference in TBBMC was largely caused by the difference in fat-free mass, whereas the difference in FFM was largely caused by the difference in glucocorticoid use based on analysis of covariance. We conclude that in patients with multiple sclerosis, physical disuse is the main determinant for the reduction in bone mass. Glucocorticoid treatment is the major determinant of the reduction in fat-free mass and thus also contributes to the reduction in bone mass.