Vertebral fractures in steroid dependent asthma and involutional osteoporosis: a comparative study

Reduced bone mass predisposes patients to the development of vertebral fractures. Measurement of bone mass by non-invasive methods is used to detect patients with involutional osteoporosis at risk from fractures. These methods have not been assessed in patients with steroid dependent osteoporosis. The objective of this study was to assess the value of a predictive fracture threshold value of bone density in patients with steroid dependent asthma.

Three groups of patients were studied. Group 1 (67 patients) had steroid dependent asthma (mean daily dose of prednisone 11.7 mg) and no vertebral fractures, group 2 (32 patients) had steroid dependent asthma (mean daily dose of prednisone 12 mg) and vertebral fractures, and group 3 (55 patients) were not taking steroids but had involutional osteoporosis and a recent non-traumatic vertebral fracture. Bone mineral density was measured by dual photon absorptiometry and vertebral fractures by radiography of the lumbar spine. A fracture threshold was determined in the two groups with fractures as the 90th percentile of the mean bone mineral density measured in the lumbar spine.

Bone mineral density was significantly higher in the steroid dependent group with fractures (group 2) than in group 3 patients, who had involutional osteoporosis and fractures (0.946 (0.18) g/cm2 v 0.830 (0.16) g/cm2). The fracture threshold value was therefore higher for patients with steroid related vertebral fractures (group 2, 1.173 g/cm2) than for those with involutional osteoporosis (group 3, 0.979 g/cm2). Vertebral fractures were more likely to occur in steroid dependent asthmatic patients with bone density above the fracture threshold value (obtained from subjects with involutional osteoporosis) than in subjects in group 3 (34% v 9%).

Vertebral fractures occur in patients treated with steroids in the presence of higher bone mineral density than is the case with patients with involutional osteoporosis. The findings suggests that the assessment of the efficacy of preventive treatment requires measurement of bone mineral density and radiology.