Urinary free cortisol excretion is associated with lumbar bone density in patients with adrenal Cushing's syndrome

Patients with adrenal Cushing's syndrome have a poor prognosis due to the autonomous hypersecretion of endogenous cortisol from the adrenal gland. Although several clinical examinations have been developed to manifest the autonomous hypersecretion of endogenous cortisol in this syndrome, it is unknown which parameter of cortisol overproduction is best associated with the adrenal cortisol content and bone and vascular complications of this syndrome. Therefore, the present study was undertaken to evaluate the parameter(s) associated with the adrenal cortisol content in patients with adrenal Cushing's syndrome, as well as to assess the associations between these parameters and the vascular and bone complications of this syndrome. Cardiovascular factors such as blood pressure and pulse rate, glucose metabolism, lipid metabolism, renal function, and indices of arteriosclerosis, except for diastolic blood pressure, failed to show an association with the adrenal cortisol content. Twenty-four-hour urinary free cortisol excretion (ρ = 0.893, P = 0.007) and plasma cortisol levels after the 1-mg (ρ = 0.857, P = 0.014) or 8-mg (ρ = 0.900, P = 0.037) overnight dexamethasone suppression test, but not plasma cortisol levels in the morning or late at night or indices of ¹³¹I-adosterol single-photon emission computed tomography-computed tomography, were significantly and positively associated with the adrenal cortisol content. Twenty-four-hour urinary free cortisol excretion, and not plasma cortisol levels after the 1- or 8-mg overnight dexamethasone suppression test, was significantly and negatively associated with lumbar spine bone density (lumbar spine bone mineral density, ρ = -0.786, P = 0.036; lumbar spine T score, ρ = -0.883, P = 0.009; and lumbar spine Z score, ρ = -0.883, P = 0.009). These results indicate that 24-h urinary free cortisol excretion is best associated with a decrease in bone density via increased adrenal cortisol overproduction and suggest that it could be used as a marker for osteoporosis in these patients.