Alterations of bone turnover and bone mass at different skeletal sites due to pure glucocorticoid excess: study in eumenorrheic patients with Cushing's syndrome

Abstract

The aim of the present investigation was to study the effect of glucocorticoid excess on bone mass and turnover not influenced by other diseases known to affect skeleton and/or by different gonadal status and sex. We studied several markers of bone turnover and bone mineral density (BMD) by both quantitative computed tomography (at spine and forearm) and dual x-ray absorptiometry (at spine and three femoral sites) in 18 eugonadal female patients affected by Cushing's syndrome (CS) compared to 24 eugonadal healthy female subjects matched for age and body mass index. In CS patients, serum bone Gla protein, a marker of osteoblastic function, was reduced (3.28 +/- 2.3 vs. 6.47 +/- 2.5; P < 0.01), and bone resorption was increased, as indicated by increased urinary hydroxyproline (36.6 +/- 12 vs. 29.0 +/- 9.1, P < 0.05) and urinary deoxypyridinoline (22.1 +/- 8.0 vs. 16.4 +/- 6.3; P < 0.05). BMD was significantly (P < 0.05 or P < 0.01) reduced at all sites, except cortical forearm, in CS patients compared to controls. By comparing z-scores of reduced BMD in CS patients, spinal trabecular BMD was found to be the most severely affected. Furthermore, disease activity, as measured by urinary free cortisol, was significantly correlated with bone Gla protein (r = -0.57; P < 0.02), urinary hydroxyproline (r = 0.57; P < 0.02), urinary deoxypyridinoline (r = 0.48, P < 0.05), and BMD measured at spine and femur. Our results show that compared to matched control subjects, female eumenorrheic CS patients have reduced osteoblastic function, increased bone resorption, and reduced BMD, and that the severity of these abnormalities is statistically related to the severity of disease activity, as indicated by urinary free cortisol. Moreover, our data suggest a site and tissue specificity of the effect of glucocorticoid excess on bone mass.