Association of urinary free cortisol with bone formation in patients with mild autonomous cortisol secretion

Context Mild autonomous cortisol secretion (ACS) is associated with an increased risk of vertebral fractures (VFx). However, the influence of this condition on bone turnover or its association with mild ACS is still controversial. Objective This study aimed to evaluate the impact of mild ACS on bone quality among patients living with the disease. Design and setting A retrospective study was conducted using data from 55 mild ACS and 12 nonfunctioning adrenal tumour (NFT) patients who visited Chiba University Hospital, Japan, from 2006 to 2018. Patients and main outcome measures We analysed clinical features and bone-related factors, including bone mineral density (BMD) and VFx, performed blood tests to assess bone metabolism markers in patients with mild ACS and NFT, and assessed the associations between bone-related markers and endocrinological parameters in patients with mild ACS. Results No significant differences between mild ACS and NFT patients were observed with respect to the presence or absence of VFx and BMD. Urinary free cortisol (UFC) was higher in mild ACS patients with VFx than those without (p = .037). The T-score and young adult mean (YAM) of the BMD of the femoral neck in mild ACS patients with a body mass index <25 were positively correlated with dehydroepiandrosterone sulphate levels (rho: 0.42, p = .017; rho: 0.40, p = .024, respectively). Pearson's correlation analysis showed that bone-specific alkaline phosphatase was negatively correlated with UFC in the patients with mild ACS (rho: -0.37, p = .026). Conclusions These results suggest that urinary free cortisol may be useful for predicting bone formation in mild ACS patients.