Oral glucocorticoid-induced fall in cortical bone volume and density in postmenopausal asthmatic patients

Despite a deepening understanding of the influence of glucocorticoids (GC) on trabecular bone, little is known about GC-induced cortical bone loss. To elucidate the mechanism of GC-induced loss of cortical bone strength with particular reference to cortical bone loss, changes in cortical density, relative cortical volume, and the Strength Strain Index (SSI) based on biomechanical analyses of the geographic distribution of cortical bone material were measured. These parameters were compared, using peripheral quantitative computed tomography (pQCT), among the following age-matched groups: 68 postmenopausal asthmatic patients receiving high-dose oral GC in addition to inhaled GC (oral GC group), 68 postmenopausal asthmatic patients receiving only inhaled GC (inhaled GC group) and 69 postmenopausal controls without asthma or GC therapy (control group). Cortical bone mineral density (BMD) was measured, relative cortical volume was obtained by dividing the cortical area by the total bone area using pQCT (Stratec XCT960), and the Strength Strain Index (SSI) was calculated in the radius based on the density distribution around the axis. Spinal fracture was assessed on lateral radiographs. The number of vertebral fractures per patient correlated highly with cortical BMD, relative cortical volume and SSI values at the radius. The number of vertebral fractures per patient and the number of patients with fracture were similar between the control and inhaled GC group, both being significantly lower than those in the oral GC group. Total BMD, trabecular BMD, cortical BMD, relative cortical volume and SSI were similar between the first two, being significantly higher than in the last group. The slopes of cortical volume-density relationship, however, were identical among the three groups, indicating the persistence of cortical bone remodeling and a similar degree of calcification regardless of GC administration.